diff --git a/README.md b/README.md
index 68e355d..b611d46 100644
--- a/README.md
+++ b/README.md
@@ -26,6 +26,25 @@ boundary.
 
 The logic lives in `static/cycle.js` and is tested in `tests/test_cycle.js`.
 
+## Notifications
+
+Web Push, sent by `notify.js` (Node, no dependencies: built-in crypto and
+SQLite). It reuses `static/cycle.js`, so reminders always match the app.
+
+- `flowtrack-notify daily` runs once a day. It sends "period expected soon"
+  once per cycle, `remindDays` (1-7, default 2) before the predicted start,
+  and "period is late" once per cycle after the expected day passes.
+- The owner turns notifications on per device in Settings, where there is
+  also a test button. On iPhone this only works from the Home Screen app
+  (iOS 16.4 or later).
+- The VAPID key pair is created on first start and stored in the database.
+  Replacing it invalidates every subscription.
+- The server only accepts subscriptions on Apple, Google, Mozilla and
+  Microsoft push hosts, because it POSTs to whatever endpoint it stores.
+
+Enable it with `--push-contact https://your.site` (the NixOS module does
+this through `push.contact`).
+
 ## Access
 
 Nginx must overwrite `Remote-User` with the Authelia username. Users listed
@@ -49,6 +68,8 @@ services.flowtrack = {
   editors = [ "kayla" ];
   viewers = [ "fred" ];
   backup.directory = "/mnt/disk2/backups/flowtrack";  # nightly, keeps 30
+  push.contact = "https://flowtrack.example.org";
+  push.time = "*-*-* 09:00:00 Europe/London";
 };
 ```
 
diff --git a/app.py b/app.py
index 76cdbb0..3895fb5 100644
--- a/app.py
+++ b/app.py
@@ -4,13 +4,17 @@
 from __future__ import annotations
 
 import argparse
+import base64
+import binascii
 import csv
 import io
 import json
 import logging
 import mimetypes
+import os
 import re
 import sqlite3
+import subprocess
 from contextlib import closing
 from datetime import date, datetime, timedelta, timezone
 from http import HTTPStatus
@@ -39,6 +43,10 @@ SYMPTOMS = (
     ("mood-swings", "Mood swings"),
 )
 SYMPTOM_IDS = frozenset(symptom_id for symptom_id, _ in SYMPTOMS)
+# The server POSTs to whatever endpoint a browser hands it, so only the real
+# push services are accepted (Apple, Google, Mozilla, Microsoft).
+PUSH_HOSTS = ("push.apple.com", "fcm.googleapis.com", "push.services.mozilla.com", "notify.windows.com")
+MAX_REMIND_DAYS = 7
 
 mimetypes.add_type("application/manifest+json", ".webmanifest")
 
@@ -76,6 +84,32 @@ def clean_entry(value: object) -> dict | None:
     return {"flow": flow, "symptoms": sorted(set(symptoms))}
 
 
+def decode_key(value: object, length: int) -> bool:
+    if not isinstance(value, str) or len(value) > 200:
+        return False
+    try:
+        return len(base64.urlsafe_b64decode(value + "=" * (-len(value) % 4))) == length
+    except (binascii.Error, ValueError):
+        return False
+
+
+def clean_subscription(value: object) -> dict | None:
+    """A browser PushSubscription.toJSON() pointing at a known push service."""
+    if not isinstance(value, dict) or not isinstance(value.get("keys"), dict):
+        return None
+    endpoint = value.get("endpoint")
+    if not isinstance(endpoint, str) or len(endpoint) > 1000:
+        return None
+    url = urlparse(endpoint)
+    host = url.hostname or ""
+    if url.scheme != "https" or not any(host == known or host.endswith("." + known) for known in PUSH_HOSTS):
+        return None
+    keys = value["keys"]
+    if not decode_key(keys.get("p256dh"), 65) or not decode_key(keys.get("auth"), 16):
+        return None
+    return {"endpoint": endpoint, "p256dh": keys["p256dh"], "auth": keys["auth"]}
+
+
 class Store:
     def __init__(self, path: str | Path):
         self.path = str(path)
@@ -102,6 +136,21 @@ class Store:
                     value TEXT NOT NULL
                 );
                 INSERT OR IGNORE INTO settings (key, value) VALUES ('share_details', 'false');
+                INSERT OR IGNORE INTO settings (key, value) VALUES ('remind_days', '2');
+                CREATE TABLE IF NOT EXISTS push_subscriptions (
+                    endpoint TEXT PRIMARY KEY,
+                    p256dh TEXT NOT NULL,
+                    auth TEXT NOT NULL,
+                    user TEXT NOT NULL,
+                    created_at TEXT NOT NULL
+                );
+                -- One row per reminder kind per cycle, so each is sent once.
+                CREATE TABLE IF NOT EXISTS notifications_sent (
+                    kind TEXT NOT NULL,
+                    cycle TEXT NOT NULL,
+                    sent_at TEXT NOT NULL,
+                    PRIMARY KEY (kind, cycle)
+                );
                 """
             )
 
@@ -110,18 +159,42 @@ class Store:
             rows = db.execute("SELECT day, flow, symptoms FROM days ORDER BY day").fetchall()
         return {row["day"]: {"flow": row["flow"], "symptoms": json.loads(row["symptoms"])} for row in rows}
 
-    def share_details(self) -> bool:
+    def setting(self, key: str) -> str | None:
         with closing(self.connect()) as db, db:
-            row = db.execute("SELECT value FROM settings WHERE key = 'share_details'").fetchone()
-        return row is not None and row["value"] == "true"
+            row = db.execute("SELECT value FROM settings WHERE key = ?", (key,)).fetchone()
+        return row["value"] if row else None
 
-    def set_share_details(self, enabled: bool) -> None:
+    def set_setting(self, key: str, value: str) -> None:
+        with closing(self.connect()) as db, db:
+            db.execute("INSERT INTO settings (key, value) VALUES (?, ?) ON CONFLICT(key) DO UPDATE SET value = excluded.value", (key, value))
+
+    def share_details(self) -> bool:
+        return self.setting("share_details") == "true"
+
+    def remind_days(self) -> int:
+        try:
+            return min(MAX_REMIND_DAYS, max(1, int(self.setting("remind_days") or 2)))
+        except ValueError:
+            return 2
+
+    def add_subscription(self, subscription: dict, user: str) -> None:
         with closing(self.connect()) as db, db:
             db.execute(
-                "UPDATE settings SET value = ? WHERE key = 'share_details'",
-                ("true" if enabled else "false",),
+                """
+                INSERT INTO push_subscriptions (endpoint, p256dh, auth, user, created_at) VALUES (?, ?, ?, ?, ?)
+                ON CONFLICT(endpoint) DO UPDATE SET p256dh = excluded.p256dh, auth = excluded.auth, user = excluded.user
+                """,
+                (subscription["endpoint"], subscription["p256dh"], subscription["auth"], user, utc_now()),
             )
 
+    def remove_subscription(self, endpoint: str) -> None:
+        with closing(self.connect()) as db, db:
+            db.execute("DELETE FROM push_subscriptions WHERE endpoint = ?", (endpoint,))
+
+    def subscription_count(self) -> int:
+        with closing(self.connect()) as db, db:
+            return db.execute("SELECT COUNT(*) FROM push_subscriptions").fetchone()[0]
+
     @staticmethod
     def _write(db: sqlite3.Connection, day: str, entry: dict, changed_at: str) -> None:
         # An empty log is the same as no log, so the row goes away.
@@ -173,12 +246,36 @@ class Store:
 class TrackerServer(ThreadingHTTPServer):
     daemon_threads = True
 
-    def __init__(self, address: tuple[str, int], store: Store, editors: set[str], viewers: set[str], dev_user: str | None = None):
+    def __init__(
+        self,
+        address: tuple[str, int],
+        store: Store,
+        editors: set[str],
+        viewers: set[str],
+        dev_user: str | None = None,
+        notify: str | None = None,
+        push_contact: str | None = None,
+    ):
         super().__init__(address, Handler)
         self.store = store
         self.editors = editors
         self.viewers = viewers
         self.dev_user = dev_user
+        # Push is sent by the flowtrack-notify (Node) helper; without it, or
+        # without a VAPID contact, the app runs with push switched off.
+        self.notify = notify if notify and push_contact else None
+        self.push_contact = push_contact
+
+    def run_notify(self, command: str) -> dict:
+        completed = subprocess.run(
+            [self.notify, command, "--database", self.store.path, "--contact", self.push_contact or ""],
+            capture_output=True,
+            text=True,
+            timeout=60,
+        )
+        if completed.returncode != 0:
+            raise RuntimeError(completed.stderr.strip() or f"flowtrack-notify {command} failed")
+        return json.loads(completed.stdout)
 
 
 class Handler(BaseHTTPRequestHandler):
@@ -235,6 +332,46 @@ class Handler(BaseHTTPRequestHandler):
             if entry["flow"] in PERIOD_FLOWS
         }
 
+    def push_state(self) -> dict:
+        store = self.server.store
+        return {
+            "available": self.server.notify is not None and store.setting("vapid_public") is not None,
+            "publicKey": store.setting("vapid_public"),
+            "remindDays": store.remind_days(),
+            "devices": store.subscription_count(),
+        }
+
+    def handle_push(self, path: str) -> None:
+        if not self.push_state()["available"]:
+            self.error_json("Notifications are not set up on the server", HTTPStatus.SERVICE_UNAVAILABLE)
+            return
+        if path == "/api/push/test":
+            try:
+                result = self.server.run_notify("test")
+            except (RuntimeError, subprocess.TimeoutExpired, json.JSONDecodeError) as error:
+                logging.error("Test notification failed: %s", error)
+                self.error_json("Sending failed on the server", HTTPStatus.BAD_GATEWAY)
+                return
+            self.json_response(result)
+            return
+        payload = self.read_json()
+        if payload is None:
+            return
+        if path == "/api/push/subscribe":
+            subscription = clean_subscription(payload)
+            if subscription is None:
+                self.error_json("Not a supported push subscription", HTTPStatus.BAD_REQUEST)
+                return
+            self.server.store.add_subscription(subscription, self.role()[0])
+            self.json_response({"devices": self.server.store.subscription_count()})
+            return
+        endpoint = payload.get("endpoint") if isinstance(payload, dict) else None
+        if not isinstance(endpoint, str):
+            self.error_json("endpoint is required", HTTPStatus.BAD_REQUEST)
+            return
+        self.server.store.remove_subscription(endpoint)
+        self.json_response({"devices": self.server.store.subscription_count()})
+
     def read_json(self) -> object:
         if self.headers.get_content_type() != "application/json":
             self.error_json("Expected application/json", HTTPStatus.UNSUPPORTED_MEDIA_TYPE)
@@ -272,6 +409,7 @@ class Handler(BaseHTTPRequestHandler):
                     "shareDetails": self.server.store.share_details(),
                     "symptoms": [{"id": symptom_id, "label": label} for symptom_id, label in SYMPTOMS],
                     "days": self.visible_days(role),
+                    "push": self.push_state() if role == "editor" else None,
                 }
             )
             return
@@ -308,12 +446,22 @@ class Handler(BaseHTTPRequestHandler):
             payload = self.read_json()
             if payload is None:
                 return
-            share = payload.get("shareDetails") if isinstance(payload, dict) else None
+            if not isinstance(payload, dict) or not payload or set(payload) - {"shareDetails", "remindDays"}:
+                self.error_json("Expected shareDetails and/or remindDays", HTTPStatus.BAD_REQUEST)
+                return
+            share = payload.get("shareDetails", False)
+            remind = payload.get("remindDays", 1)
             if not isinstance(share, bool):
                 self.error_json("shareDetails must be boolean", HTTPStatus.BAD_REQUEST)
                 return
-            self.server.store.set_share_details(share)
-            self.json_response({"shareDetails": share})
+            if not isinstance(remind, int) or isinstance(remind, bool) or not 1 <= remind <= MAX_REMIND_DAYS:
+                self.error_json(f"remindDays must be 1-{MAX_REMIND_DAYS}", HTTPStatus.BAD_REQUEST)
+                return
+            if "shareDetails" in payload:
+                self.server.store.set_setting("share_details", "true" if share else "false")
+            if "remindDays" in payload:
+                self.server.store.set_setting("remind_days", str(remind))
+            self.json_response({"shareDetails": self.server.store.share_details(), "remindDays": self.server.store.remind_days()})
             return
         self.error_json("Not found", HTTPStatus.NOT_FOUND)
 
@@ -323,6 +471,9 @@ class Handler(BaseHTTPRequestHandler):
         if role != "editor":
             self.error_json("Read-only access", HTTPStatus.FORBIDDEN)
             return
+        if path in ("/api/push/subscribe", "/api/push/unsubscribe", "/api/push/test"):
+            self.handle_push(path)
+            return
         if path != "/api/days":
             self.error_json("Not found", HTTPStatus.NOT_FOUND)
             return
@@ -403,6 +554,8 @@ def main() -> None:
     parser.add_argument("--dev-user", help="identity to assume when no Remote-User header is sent (local testing only)")
     parser.add_argument("--backup-to", type=Path, help="write a snapshot of the database to this directory and exit")
     parser.add_argument("--keep", type=int, default=30, help="snapshots to keep with --backup-to")
+    parser.add_argument("--push-contact", help="VAPID contact (https: or mailto: URL); enables push notifications")
+    parser.add_argument("--notify", default=os.environ.get("FLOWTRACK_NOTIFY"), help="path to flowtrack-notify")
     args = parser.parse_args()
 
     logging.basicConfig(level=logging.INFO, format="%(asctime)s %(levelname)s %(message)s")
@@ -412,7 +565,13 @@ def main() -> None:
     if args.backup_to:
         logging.info("Wrote %s", store.backup(args.backup_to, args.keep))
         return
-    server = TrackerServer((args.host, args.port), store, set(args.editor), set(args.viewer), args.dev_user)
+    server = TrackerServer(
+        (args.host, args.port), store, set(args.editor), set(args.viewer), args.dev_user, args.notify, args.push_contact
+    )
+    if server.notify:
+        # Creates the VAPID key pair on first start; the browser needs its
+        # public half before it can subscribe.
+        server.run_notify("init")
     logging.info("Listening on http://%s:%s", args.host, args.port)
     server.serve_forever()
 
diff --git a/flake.nix b/flake.nix
index 7c1ce7c..68dab10 100644
--- a/flake.nix
+++ b/flake.nix
@@ -30,7 +30,10 @@
             python3 -m py_compile app.py
             node --check static/app.js
             node --check static/cycle.js
+            node --check static/sw.js
+            node --check notify.js
             node tests/test_cycle.js
+            node --disable-warning=ExperimentalWarning tests/test_push.js
             touch $out
           '';
         });
diff --git a/module.nix b/module.nix
index f73e128..b3a0665 100644
--- a/module.nix
+++ b/module.nix
@@ -20,6 +20,7 @@ let
   };
   userFlags = lib.concatMapStringsSep " " (user: "--editor ${lib.escapeShellArg user}") cfg.editors
     + " " + lib.concatMapStringsSep " " (user: "--viewer ${lib.escapeShellArg user}") cfg.viewers;
+  pushFlag = lib.optionalString (cfg.push.contact != null) " --push-contact ${lib.escapeShellArg cfg.push.contact}";
 in
 {
   options.services.flowtrack = {
@@ -45,6 +46,18 @@ in
       default = [ ];
       description = "Remote-User names with read-only access.";
     };
+    push.contact = lib.mkOption {
+      type = lib.types.nullOr lib.types.str;
+      default = null;
+      example = "https://flowtrack.example.org";
+      description = "VAPID contact URL (https: or mailto:) sent to push services; null disables push notifications.";
+    };
+    push.time = lib.mkOption {
+      type = lib.types.str;
+      default = "*-*-* 09:00:00";
+      example = "*-*-* 09:00:00 Europe/London";
+      description = "systemd OnCalendar expression for the daily reminder check.";
+    };
     backup = {
       directory = lib.mkOption {
         type = lib.types.nullOr lib.types.str;
@@ -73,12 +86,31 @@ in
         wantedBy = [ "multi-user.target" ];
         after = [ "network.target" ];
         serviceConfig = hardening // {
-          ExecStart = "${cfg.package}/bin/flowtrack --host 127.0.0.1 --port ${toString cfg.port} --database ${database} ${userFlags}";
+          ExecStart = "${cfg.package}/bin/flowtrack --host 127.0.0.1 --port ${toString cfg.port} --database ${database} ${userFlags}${pushFlag}";
           Restart = "on-failure";
           RestartSec = 3;
         };
       };
     }
+    (lib.mkIf (cfg.push.contact != null) {
+      systemd.services.flowtrack-notify = {
+        description = "Send due Flowtrack reminders";
+        after = [ "network-online.target" "flowtrack.service" ];
+        wants = [ "network-online.target" ];
+        serviceConfig = hardening // {
+          Type = "oneshot";
+          ExecStart = "${cfg.package}/bin/flowtrack-notify daily --database ${database} --contact ${lib.escapeShellArg cfg.push.contact}";
+        };
+      };
+
+      systemd.timers.flowtrack-notify = {
+        wantedBy = [ "timers.target" ];
+        timerConfig = {
+          OnCalendar = cfg.push.time;
+          Persistent = true;
+        };
+      };
+    })
     (lib.mkIf (cfg.backup.directory != null) {
       systemd.tmpfiles.rules = [ "d ${cfg.backup.directory} 0700 flowtrack flowtrack -" ];
 
diff --git a/notify.js b/notify.js
new file mode 100644
index 0000000..c66f7bd
--- /dev/null
+++ b/notify.js
@@ -0,0 +1,209 @@
+#!/usr/bin/env node
+// Web Push for Flowtrack: VAPID keys, payload encryption (RFC 8291) and the
+// daily "period soon / late" check. Dependency-free: Node's own crypto and
+// SQLite. The schema is owned by app.py, which always initializes it first.
+"use strict";
+
+const crypto = require("node:crypto");
+const path = require("node:path");
+const Cycle = require(path.join(__dirname, "static", "cycle.js"));
+
+const b64url = {
+  encode: bytes => Buffer.from(bytes).toString("base64url"),
+  decode: text => Buffer.from(text, "base64url")
+};
+const formatDay = number =>
+  new Date(number * 86400000).toLocaleDateString("en-GB", { weekday: "short", day: "numeric", month: "short", timeZone: "UTC" });
+const localIso = () => {
+  const now = new Date();
+  return `${now.getFullYear()}-${String(now.getMonth() + 1).padStart(2, "0")}-${String(now.getDate()).padStart(2, "0")}`;
+};
+
+function openDatabase(file) {
+  const { DatabaseSync } = require("node:sqlite");
+  const db = new DatabaseSync(file);
+  db.exec("PRAGMA busy_timeout=10000");
+  return db;
+}
+
+const setting = (db, key) => {
+  const row = db.prepare("SELECT value FROM settings WHERE key = ?").get(key);
+  return row ? row.value : null;
+};
+
+// Generated once and kept in the database: browsers bind each subscription
+// to this key, so replacing it would silently break every subscribed device.
+function vapidKeys(db) {
+  if (!setting(db, "vapid_private")) {
+    const { privateKey } = crypto.generateKeyPairSync("ec", { namedCurve: "prime256v1" });
+    const jwk = privateKey.export({ format: "jwk" });
+    const insert = db.prepare("INSERT OR IGNORE INTO settings (key, value) VALUES (?, ?)");
+    insert.run("vapid_private", JSON.stringify(jwk));
+    insert.run("vapid_public", b64url.encode(Buffer.concat([Buffer.from([4]), b64url.decode(jwk.x), b64url.decode(jwk.y)])));
+  }
+  return {
+    privateKey: crypto.createPrivateKey({ key: JSON.parse(setting(db, "vapid_private")), format: "jwk" }),
+    publicKey: setting(db, "vapid_public")
+  };
+}
+
+function vapidAuthorization(endpoint, keys, contact, now = Date.now()) {
+  const header = b64url.encode(JSON.stringify({ typ: "JWT", alg: "ES256" }));
+  const claims = b64url.encode(JSON.stringify({
+    aud: new URL(endpoint).origin,
+    exp: Math.floor(now / 1000) + 12 * 3600,
+    sub: contact
+  }));
+  const signature = crypto.sign("sha256", Buffer.from(`${header}.${claims}`), { key: keys.privateKey, dsaEncoding: "ieee-p1363" });
+  return `vapid t=${header}.${claims}.${b64url.encode(signature)}, k=${keys.publicKey}`;
+}
+
+// RFC 8291 "aes128gcm": one record holding the whole payload.
+function encrypt(payload, subscriberKey, authSecret) {
+  const receiver = b64url.decode(subscriberKey);
+  const auth = b64url.decode(authSecret);
+  const sender = crypto.createECDH("prime256v1");
+  const senderKey = sender.generateKeys();
+  const shared = sender.computeSecret(receiver);
+  const keyInfo = Buffer.concat([Buffer.from("WebPush: info\0"), receiver, senderKey]);
+  const ikm = Buffer.from(crypto.hkdfSync("sha256", shared, auth, keyInfo, 32));
+  const salt = crypto.randomBytes(16);
+  const cek = Buffer.from(crypto.hkdfSync("sha256", ikm, salt, Buffer.from("Content-Encoding: aes128gcm\0"), 16));
+  const nonce = Buffer.from(crypto.hkdfSync("sha256", ikm, salt, Buffer.from("Content-Encoding: nonce\0"), 12));
+  const cipher = crypto.createCipheriv("aes-128-gcm", cek, nonce);
+  // 0x02 marks the last (and only) record.
+  const body = Buffer.concat([cipher.update(Buffer.concat([Buffer.from(payload), Buffer.from([2])])), cipher.final(), cipher.getAuthTag()]);
+  const header = Buffer.alloc(21);
+  salt.copy(header, 0);
+  header.writeUInt32BE(4096, 16);
+  header.writeUInt8(senderKey.length, 20);
+  return Buffer.concat([header, senderKey, body]);
+}
+
+async function sendAll(db, contact, message) {
+  const keys = vapidKeys(db);
+  const subscriptions = db.prepare("SELECT endpoint, p256dh, auth FROM push_subscriptions").all();
+  const result = { sent: 0, failed: 0, removed: 0, errors: [] };
+  const payload = JSON.stringify(message);
+  for (const subscription of subscriptions) {
+    try {
+      const response = await fetch(subscription.endpoint, {
+        method: "POST",
+        headers: {
+          Authorization: vapidAuthorization(subscription.endpoint, keys, contact),
+          "Content-Encoding": "aes128gcm",
+          "Content-Type": "application/octet-stream",
+          TTL: String(message.ttl || 86400),
+          Urgency: "normal"
+        },
+        body: encrypt(payload, subscription.p256dh, subscription.auth),
+        signal: AbortSignal.timeout(20000)
+      });
+      if (response.ok) {
+        result.sent += 1;
+      } else if (response.status === 404 || response.status === 410) {
+        // The device unsubscribed or the app was removed from the home screen.
+        db.prepare("DELETE FROM push_subscriptions WHERE endpoint = ?").run(subscription.endpoint);
+        result.removed += 1;
+      } else {
+        result.failed += 1;
+        result.errors.push(`${new URL(subscription.endpoint).host}: ${response.status} ${(await response.text()).slice(0, 200)}`);
+      }
+    } catch (error) {
+      result.failed += 1;
+      result.errors.push(`${new URL(subscription.endpoint).host}: ${error.message}`);
+    }
+  }
+  return result;
+}
+
+// Which reminder, if any, is due today. Each kind is sent at most once per
+// cycle (keyed on the cycle's start date), so a missed timer run or a second
+// run on the same day never repeats it.
+function dueReminder(summary, remindDays) {
+  const { current, predictions, late, today } = summary;
+  if (!current || current.onPeriod) return null;
+  const cycle = Cycle.toIso(current.start);
+  if (late > 0) {
+    return {
+      kind: "late",
+      cycle,
+      title: "Period is late",
+      body: `It was expected on ${formatDay(today - late)}. Log it in Flowtrack when it starts.`
+    };
+  }
+  const next = predictions[0];
+  const until = next.start - today;
+  if (until < 1 || until > remindDays) return null;
+  return {
+    kind: "soon",
+    cycle,
+    title: "Period expected soon",
+    body: until === 1
+      ? `Your period is expected tomorrow, ${formatDay(next.start)}.`
+      : `Your period is expected in about ${until} days, around ${formatDay(next.start)}.`
+  };
+}
+
+async function daily(db, contact, todayIso) {
+  const days = {};
+  for (const row of db.prepare("SELECT day, flow, symptoms FROM days").all()) {
+    days[row.day] = { flow: row.flow, symptoms: JSON.parse(row.symptoms) };
+  }
+  const remindDays = Number(setting(db, "remind_days")) || 2;
+  const reminder = dueReminder(Cycle.summarize(days, todayIso), remindDays);
+  if (!reminder) return { due: null };
+  if (db.prepare("SELECT 1 FROM notifications_sent WHERE kind = ? AND cycle = ?").get(reminder.kind, reminder.cycle)) {
+    return { due: reminder.kind, alreadySent: true };
+  }
+  const result = await sendAll(db, contact, { title: reminder.title, body: reminder.body, tag: reminder.kind, url: "/" });
+  // Only mark it sent once a device got it, so subscribing later the same
+  // day still delivers it on the next run.
+  if (result.sent) {
+    db.prepare("INSERT OR IGNORE INTO notifications_sent (kind, cycle, sent_at) VALUES (?, ?, ?)")
+      .run(reminder.kind, reminder.cycle, new Date().toISOString());
+  }
+  return { due: reminder.kind, ...result };
+}
+
+function parseArgs(argv) {
+  const [command, ...rest] = argv;
+  const options = { command };
+  for (let index = 0; index < rest.length; index += 2) {
+    if (!rest[index].startsWith("--")) throw new Error(`Unexpected argument ${rest[index]}`);
+    options[rest[index].slice(2)] = rest[index + 1];
+  }
+  return options;
+}
+
+async function main(argv) {
+  const options = parseArgs(argv);
+  if (!options.database) throw new Error("--database is required");
+  const db = openDatabase(options.database);
+  try {
+    if (options.command === "init") return { publicKey: vapidKeys(db).publicKey };
+    if (!options.contact) throw new Error("--contact is required");
+    if (options.command === "test") {
+      return await sendAll(db, options.contact, {
+        title: "Flowtrack",
+        body: "Test notification: reminders will arrive like this.",
+        tag: "test",
+        url: "/",
+        ttl: 600
+      });
+    }
+    if (options.command === "daily") return await daily(db, options.contact, options.today || localIso());
+    throw new Error("usage: flowtrack-notify init|test|daily --database DB [--contact URL] [--today YYYY-MM-DD]");
+  } finally {
+    db.close();
+  }
+}
+
+if (require.main === module) {
+  main(process.argv.slice(2)).then(
+    result => { console.log(JSON.stringify(result)); },
+    error => { console.error(error.message); process.exitCode = 1; }
+  );
+}
+
+module.exports = { b64url, encrypt, vapidKeys, vapidAuthorization, dueReminder, main };
diff --git a/package.nix b/package.nix
index 4e89347..dccb368 100644
--- a/package.nix
+++ b/package.nix
@@ -1,8 +1,8 @@
-{ lib, stdenvNoCC, makeWrapper, python3 }:
+{ lib, stdenvNoCC, makeWrapper, python3, nodejs-slim }:
 
 stdenvNoCC.mkDerivation {
   pname = "flowtrack";
-  version = "1.1.0";
+  version = "1.2.0";
   src = ./.;
 
   nativeBuildInputs = [ makeWrapper ];
@@ -10,10 +10,14 @@ stdenvNoCC.mkDerivation {
   installPhase = ''
     runHook preInstall
     mkdir -p $out/share/flowtrack $out/bin
-    cp app.py $out/share/flowtrack/app.py
+    cp app.py notify.js $out/share/flowtrack/
     cp -r static $out/share/flowtrack/static
+    # node:sqlite still prints an ExperimentalWarning on every start.
+    makeWrapper ${nodejs-slim}/bin/node $out/bin/flowtrack-notify \
+      --add-flags "--disable-warning=ExperimentalWarning $out/share/flowtrack/notify.js"
     makeWrapper ${python3}/bin/python3 $out/bin/flowtrack \
-      --add-flags "$out/share/flowtrack/app.py"
+      --add-flags "$out/share/flowtrack/app.py" \
+      --set-default FLOWTRACK_NOTIFY $out/bin/flowtrack-notify
     runHook postInstall
   '';
 
diff --git a/static/app.js b/static/app.js
index a14e3bf..5e86d6f 100644
--- a/static/app.js
+++ b/static/app.js
@@ -14,7 +14,10 @@
     days: {},
     view: "today",
     month: null,
-    sheetDay: null
+    sheetDay: null,
+    push: null,
+    // This device's PushSubscription: undefined until checked, then null or set.
+    device: undefined
   };
 
   const $ = id => document.getElementById(id);
@@ -79,10 +82,12 @@
         role: payload.role,
         shareDetails: payload.shareDetails,
         symptoms: payload.symptoms,
-        days: payload.days
+        days: payload.days,
+        push: payload.push
       });
       if (!$("banner").classList.contains("error")) showBanner("");
       render();
+      if (state.device === undefined) await checkDevice();
     } catch (error) {
       showBanner(error.message === "Not allowed" ? "This account does not have access to Flowtrack." : error.message, true);
     }
@@ -507,7 +512,151 @@
 
   // ---- Settings ------------------------------------------------------------
 
+  // ---- Notifications -------------------------------------------------------
+
+  const isIos = () => /iPhone|iPad|iPod/.test(navigator.userAgent) || (navigator.platform === "MacIntel" && navigator.maxTouchPoints > 1);
+  const installed = () => window.navigator.standalone === true || window.matchMedia("(display-mode: standalone)").matches;
+  const pushSupported = () => "serviceWorker" in navigator && "PushManager" in window && "Notification" in window;
+  const keyBytes = key => Uint8Array.from(atob(key.replace(/-/g, "+").replace(/_/g, "/")), char => char.charCodeAt(0));
+  const keyText = buffer => btoa(String.fromCharCode(...new Uint8Array(buffer))).replace(/\+/g, "-").replace(/\//g, "_").replace(/=+$/, "");
+  // serviceWorker.ready never settles if registration failed, so give up.
+  const workerReady = () => Promise.race([
+    navigator.serviceWorker.ready,
+    new Promise((_, reject) => setTimeout(() => reject(new Error("the notification worker did not start")), 8000))
+  ]);
+
+  async function checkDevice() {
+    if (!editable() || !state.push || !state.push.available || !pushSupported()) {
+      state.device = null;
+      return;
+    }
+    try {
+      const registration = await workerReady();
+      let subscription = await registration.pushManager.getSubscription();
+      // A subscription made for a different server key can never be
+      // delivered to, so drop it rather than show notifications as on.
+      if (subscription && subscription.options.applicationServerKey &&
+          keyText(subscription.options.applicationServerKey) !== state.push.publicKey) {
+        await subscription.unsubscribe();
+        subscription = null;
+      }
+      // Re-register on every launch so the server copy survives a restore.
+      if (subscription) await sendJson("POST", "/api/push/subscribe", subscription.toJSON());
+      state.device = subscription;
+    } catch {
+      state.device = null;
+    }
+    render();
+  }
+
+  async function enablePush() {
+    try {
+      // iOS only shows the permission prompt straight from a tap, so this
+      // must be the first thing awaited in the click handler.
+      const permission = await Notification.requestPermission();
+      if (permission !== "granted") {
+        showBanner("Notifications were not allowed.", true);
+        render();
+        return;
+      }
+      const registration = await workerReady();
+      const subscription = await registration.pushManager.subscribe({
+        userVisibleOnly: true,
+        applicationServerKey: keyBytes(state.push.publicKey)
+      });
+      const { devices } = await sendJson("POST", "/api/push/subscribe", subscription.toJSON());
+      state.device = subscription;
+      state.push.devices = devices;
+      showBanner("Notifications are on. Send a test to check.");
+    } catch (error) {
+      showBanner(`Couldn't turn on notifications: ${error.message}`, true);
+    }
+    render();
+  }
+
+  async function disablePush() {
+    try {
+      const { devices } = await sendJson("POST", "/api/push/unsubscribe", { endpoint: state.device.endpoint });
+      await state.device.unsubscribe();
+      state.device = null;
+      state.push.devices = devices;
+      showBanner("Notifications are off on this device.");
+    } catch (error) {
+      showBanner(`Couldn't turn off notifications: ${error.message}`, true);
+    }
+    render();
+  }
+
+  async function testPush(button) {
+    button.disabled = true;
+    try {
+      const result = await api("/api/push/test", { method: "POST" });
+      if (result.sent) showBanner(`Test sent to ${plural(result.sent, "device")}. It should arrive within a few seconds.`);
+      else showBanner(result.errors[0] ? `Test failed: ${result.errors[0]}` : "No devices are signed up for notifications.", true);
+    } catch (error) {
+      showBanner(`Test failed: ${error.message}`, true);
+    } finally {
+      button.disabled = false;
+    }
+  }
+
+  async function setRemindDays(remindDays) {
+    try {
+      await sendJson("PUT", "/api/settings", { remindDays });
+      state.push.remindDays = remindDays;
+      showBanner(`You'll be reminded ${plural(remindDays, "day")} before.`);
+      render();
+    } catch (error) {
+      showBanner(`Couldn't save: ${error.message}`, true);
+    }
+  }
+
+  function renderNotifications() {
+    const body = $("notify-body");
+    const note = text => h("p", { class: "notify-note" }, text);
+    if (!state.push || !state.push.available) {
+      body.replaceChildren(note("Notifications are not set up on the server yet."));
+      return;
+    }
+    if (!pushSupported()) {
+      body.replaceChildren(note(isIos() && !installed()
+        ? "On iPhone, notifications only work from the Home Screen app. In Safari tap Share, then Add to Home Screen, and open Flowtrack from there."
+        : "This browser does not support notifications."));
+      return;
+    }
+    if (Notification.permission === "denied") {
+      body.replaceChildren(note(isIos()
+        ? "Notifications are blocked. Turn them on in the iPhone Settings app under Notifications, Flowtrack."
+        : "Notifications are blocked for this site in the browser settings."));
+      return;
+    }
+    if (state.device === undefined) {
+      body.replaceChildren(note("Checking…"));
+      return;
+    }
+    const days = h("select", { "aria-label": "Days before" }, range(1, 7).map(count =>
+      h("option", { value: String(count), selected: count === state.push.remindDays }, String(count))
+    ));
+    days.addEventListener("change", () => setRemindDays(Number(days.value)));
+    const remind = h("label", { class: "remind-row" }, "Remind me", days, state.push.remindDays === 1 ? "day before" : "days before");
+    if (!state.device) {
+      body.replaceChildren(
+        h("button", { type: "button", class: "button", onclick: enablePush }, "Turn on notifications"),
+        remind
+      );
+      return;
+    }
+    const test = h("button", { type: "button", class: "button" }, "Send test notification");
+    test.addEventListener("click", () => testPush(test));
+    body.replaceChildren(
+      h("p", { class: "notify-status" }, h("span", { class: "status-dot" }), "On for this device"),
+      remind,
+      h("div", { class: "button-row" }, test, h("button", { type: "button", class: "button secondary", onclick: disablePush }, "Turn off"))
+    );
+  }
+
   function renderSettings(summary) {
+    renderNotifications();
     $("share-toggle").checked = state.shareDetails;
     const hint = summary.periodSamples
       ? `Leave "Ended" empty to use the average length so far, ${plural(summary.periodLength, "day")}.`
@@ -572,6 +721,7 @@
     }
   });
   seedForm($("seed-form"));
+  if ("serviceWorker" in navigator) navigator.serviceWorker.register("/sw.js").catch(() => {});
   // The home-screen app is often resumed rather than reopened, so refresh
   // whenever it comes back to the foreground (this also rolls "today" over).
   document.addEventListener("visibilitychange", () => {
diff --git a/static/index.html b/static/index.html
index 40b6dea..80cfa02 100644
--- a/static/index.html
+++ b/static/index.html
@@ -14,7 +14,7 @@
     <link rel="manifest" href="/manifest.webmanifest" crossorigin="use-credentials">
     <link rel="icon" href="/icon.svg" type="image/svg+xml">
     <link rel="apple-touch-icon" href="/apple-touch-icon.png">
-    <link rel="stylesheet" href="/styles.css?v=1.1.0">
+    <link rel="stylesheet" href="/styles.css?v=1.2.0">
   </head>
   <body>
     <header class="topbar">
@@ -74,6 +74,11 @@
       </section>
 
       <section class="view" id="view-settings" aria-labelledby="tab-settings" hidden>
+        <div class="card" id="notify-card">
+          <h2>Notifications</h2>
+          <p class="subtitle">A reminder before your period is due, and a note if it is late.</p>
+          <div id="notify-body" class="notify-body"></div>
+        </div>
         <div class="card" id="share-card">
           <h2>Sharing</h2>
           <label class="switch-row">
@@ -125,7 +130,7 @@
       </form>
     </dialog>
 
-    <script src="/cycle.js?v=1.1.0"></script>
-    <script src="/app.js?v=1.1.0"></script>
+    <script src="/cycle.js?v=1.2.0"></script>
+    <script src="/app.js?v=1.2.0"></script>
   </body>
 </html>
diff --git a/static/styles.css b/static/styles.css
index 78b519f..bf0e495 100644
--- a/static/styles.css
+++ b/static/styles.css
@@ -307,6 +307,19 @@ main {
 .switch-row small { color: var(--muted); font-size: 0.85rem; }
 .switch-row input { flex: none; width: 24px; height: 24px; accent-color: var(--period); }
 
+.notify-body { display: grid; gap: 14px; justify-items: start; }
+.notify-note { margin: 0; color: var(--ink-2); font-size: 0.92rem; }
+.notify-status { display: flex; align-items: center; gap: 8px; margin: 0; font-weight: 600; }
+.status-dot { width: 10px; height: 10px; border-radius: 999px; background: var(--fertile); }
+.remind-row { display: flex; align-items: center; gap: 8px; color: var(--ink-2); font-size: 0.92rem; }
+.remind-row select {
+  min-height: 40px;
+  padding: 6px 10px;
+  border: 1.5px solid var(--line);
+  border-radius: 10px;
+  background: var(--surface);
+}
+
 .seed-form { display: grid; gap: 12px; }
 .seed-form label { display: grid; gap: 4px; color: var(--ink-2); font-size: 0.88rem; font-weight: 600; }
 .seed-form input {
diff --git a/static/sw.js b/static/sw.js
new file mode 100644
index 0000000..76f8112
--- /dev/null
+++ b/static/sw.js
@@ -0,0 +1,29 @@
+// Service worker: only shows push notifications. It deliberately caches
+// nothing, so the app always loads fresh from the server.
+self.addEventListener("install", () => self.skipWaiting());
+self.addEventListener("activate", event => event.waitUntil(self.clients.claim()));
+
+self.addEventListener("push", event => {
+  let message = { title: "Flowtrack", body: "" };
+  try {
+    message = { ...message, ...event.data.json() };
+  } catch {
+    // An empty or unreadable push still has to show something on iOS.
+  }
+  event.waitUntil(self.registration.showNotification(message.title, {
+    body: message.body,
+    icon: "/icon-192.png",
+    badge: "/icon-192.png",
+    tag: message.tag,
+    data: { url: message.url || "/" }
+  }));
+});
+
+self.addEventListener("notificationclick", event => {
+  event.notification.close();
+  event.waitUntil((async () => {
+    const windows = await self.clients.matchAll({ type: "window", includeUncontrolled: true });
+    if (windows.length) return windows[0].focus();
+    return self.clients.openWindow(event.notification.data.url);
+  })());
+});
diff --git a/tests/test_app.py b/tests/test_app.py
index cba7066..7a7b1f2 100644
--- a/tests/test_app.py
+++ b/tests/test_app.py
@@ -1,5 +1,7 @@
+import base64
 import json
 import sqlite3
+import sys
 import tempfile
 import threading
 import unittest
@@ -138,6 +140,21 @@ class ServerTests(unittest.TestCase):
         }})
         self.assertEqual((status, result), (200, {"added": 2}))
 
+    def test_push_is_off_without_a_helper(self):
+        _, state = self.request("GET", "/api/state", user="kayla")
+        self.assertFalse(state["push"]["available"])
+        self.assertEqual(self.request("POST", "/api/push/test", user="kayla")[0], 503)
+        _, state = self.request("GET", "/api/state", user="fred")
+        self.assertIsNone(state["push"])
+
+    def test_remind_days_setting(self):
+        self.assertEqual(self.request("PUT", "/api/settings", user="kayla", body={"remindDays": 3})[1], {"shareDetails": False, "remindDays": 3})
+        self.assertEqual(self.request("PUT", "/api/settings", user="kayla", body={"remindDays": 9})[0], 400)
+        self.assertEqual(self.request("PUT", "/api/settings", user="kayla", body={"remindDays": True})[0], 400)
+        self.assertEqual(self.request("PUT", "/api/settings", user="kayla", body={"other": 1})[0], 400)
+        _, state = self.request("GET", "/api/state", user="kayla")
+        self.assertEqual(state["push"]["remindDays"], 3)
+
     def test_static_files(self):
         status, body = self.request("GET", "/")
         self.assertEqual(status, 200)
@@ -146,5 +163,62 @@ class ServerTests(unittest.TestCase):
         self.assertEqual(self.request("GET", "/manifest.webmanifest")[0], 200)
 
 
+FAKE_NOTIFY = """#!{python}
+import json, sqlite3, sys
+command, database = sys.argv[1], sys.argv[3]
+if command == "init":
+    with sqlite3.connect(database) as db:
+        db.execute("INSERT OR IGNORE INTO settings VALUES ('vapid_public', 'PUBLIC')")
+    print(json.dumps({{"publicKey": "PUBLIC"}}))
+else:
+    print(json.dumps({{"sent": 1, "failed": 0, "removed": 0, "errors": [], "contact": sys.argv[5]}}))
+"""
+
+APPLE_SUBSCRIPTION = {
+    "endpoint": "https://web.push.apple.com/QGuQyavXutnMH",
+    "keys": {"p256dh": base64.urlsafe_b64encode(b"\x04" + b"k" * 64).decode().rstrip("="), "auth": base64.urlsafe_b64encode(b"a" * 16).decode().rstrip("=")},
+}
+
+
+class PushServerTests(ServerTests):
+    def setUp(self):
+        super().setUp()
+        script = Path(self.temp.name) / "notify"
+        script.write_text(FAKE_NOTIFY.format(python=sys.executable))
+        script.chmod(0o755)
+        self.server.notify = str(script)
+        self.server.push_contact = "https://flowtrack.example.org"
+        self.server.run_notify("init")
+
+    # Every other server test also runs again with push switched on.
+    test_push_is_off_without_a_helper = None
+
+    def test_push_state(self):
+        _, state = self.request("GET", "/api/state", user="kayla")
+        self.assertEqual(state["push"], {"available": True, "publicKey": "PUBLIC", "remindDays": 2, "devices": 0})
+
+    def test_subscribe_test_and_unsubscribe(self):
+        self.assertEqual(self.request("POST", "/api/push/subscribe", user="kayla", body=APPLE_SUBSCRIPTION), (200, {"devices": 1}))
+        self.assertEqual(self.request("POST", "/api/push/subscribe", user="kayla", body=APPLE_SUBSCRIPTION), (200, {"devices": 1}))
+        status, result = self.request("POST", "/api/push/test", user="kayla")
+        self.assertEqual((status, result["sent"], result["contact"]), (200, 1, "https://flowtrack.example.org"))
+        self.assertEqual(self.request("POST", "/api/push/test", user="fred")[0], 403)
+        self.assertEqual(self.request("POST", "/api/push/unsubscribe", user="kayla", body={"endpoint": APPLE_SUBSCRIPTION["endpoint"]}), (200, {"devices": 0}))
+
+    def test_only_real_push_services(self):
+        for endpoint in (
+            "https://127.0.0.1/push",
+            "http://web.push.apple.com/x",
+            "https://evilpush.apple.com.example.org/x",
+            "https://router.nordhammer.it/api",
+        ):
+            body = {**APPLE_SUBSCRIPTION, "endpoint": endpoint}
+            self.assertEqual(self.request("POST", "/api/push/subscribe", user="kayla", body=body)[0], 400, endpoint)
+        bad_keys = {**APPLE_SUBSCRIPTION, "keys": {"p256dh": "short", "auth": APPLE_SUBSCRIPTION["keys"]["auth"]}}
+        self.assertEqual(self.request("POST", "/api/push/subscribe", user="kayla", body=bad_keys)[0], 400)
+        self.assertEqual(self.request("POST", "/api/push/subscribe", user="fred", body=APPLE_SUBSCRIPTION)[0], 403)
+        self.assertEqual(self.request("POST", "/api/push/subscribe", user="kayla", body={**APPLE_SUBSCRIPTION, "endpoint": "https://fcm.googleapis.com/fcm/send/abc"})[0], 200)
+
+
 if __name__ == "__main__":
     unittest.main()
diff --git a/tests/test_push.js b/tests/test_push.js
new file mode 100644
index 0000000..6f32598
--- /dev/null
+++ b/tests/test_push.js
@@ -0,0 +1,152 @@
+const assert = require("node:assert/strict");
+const crypto = require("node:crypto");
+const http = require("node:http");
+const fs = require("node:fs");
+const os = require("node:os");
+const path = require("node:path");
+const { execFileSync } = require("node:child_process");
+const { DatabaseSync } = require("node:sqlite");
+const push = require("../notify.js");
+const cycle = require("../static/cycle.js");
+
+const { b64url } = push;
+
+// Decrypts like the receiving browser does (RFC 8291), using its private key.
+function decrypt(body, receiver, auth) {
+  const salt = body.subarray(0, 16);
+  const keyLength = body.readUInt8(20);
+  const senderKey = body.subarray(21, 21 + keyLength);
+  const shared = receiver.computeSecret(senderKey);
+  const keyInfo = Buffer.concat([Buffer.from("WebPush: info\0"), receiver.getPublicKey(), senderKey]);
+  const ikm = Buffer.from(crypto.hkdfSync("sha256", shared, auth, keyInfo, 32));
+  const cek = Buffer.from(crypto.hkdfSync("sha256", ikm, salt, Buffer.from("Content-Encoding: aes128gcm\0"), 16));
+  const nonce = Buffer.from(crypto.hkdfSync("sha256", ikm, salt, Buffer.from("Content-Encoding: nonce\0"), 12));
+  const record = body.subarray(21 + keyLength);
+  const decipher = crypto.createDecipheriv("aes-128-gcm", cek, nonce);
+  decipher.setAuthTag(record.subarray(record.length - 16));
+  const plain = Buffer.concat([decipher.update(record.subarray(0, record.length - 16)), decipher.final()]);
+  assert.equal(plain[plain.length - 1], 2, "last-record delimiter");
+  return plain.subarray(0, plain.length - 1).toString();
+}
+
+function device() {
+  const receiver = crypto.createECDH("prime256v1");
+  receiver.generateKeys();
+  const auth = crypto.randomBytes(16);
+  return { receiver, auth, p256dh: b64url.encode(receiver.getPublicKey()), authText: b64url.encode(auth) };
+}
+
+function verifyVapid(authorization, publicKey, audience) {
+  const [, token, key] = authorization.match(/^vapid t=([^,]+), k=(.+)$/);
+  assert.equal(key, publicKey);
+  const [header, claims, signature] = token.split(".");
+  const raw = b64url.decode(publicKey);
+  const verifier = crypto.createPublicKey({
+    key: { kty: "EC", crv: "P-256", x: b64url.encode(raw.subarray(1, 33)), y: b64url.encode(raw.subarray(33)) },
+    format: "jwk"
+  });
+  assert.ok(crypto.verify("sha256", Buffer.from(`${header}.${claims}`), { key: verifier, dsaEncoding: "ieee-p1363" }, b64url.decode(signature)));
+  const parsed = JSON.parse(b64url.decode(claims));
+  assert.equal(parsed.aud, audience);
+  assert.ok(parsed.exp > Date.now() / 1000 && parsed.exp <= Date.now() / 1000 + 24 * 3600, "exp within 24h");
+  return parsed;
+}
+
+function logPeriods(starts, length = 5) {
+  const days = {};
+  for (const start of starts) {
+    for (let offset = 0; offset < length; offset += 1) days[cycle.toIso(cycle.toDay(start) + offset)] = { flow: "medium", symptoms: [] };
+  }
+  return days;
+}
+
+(async () => {
+  // Encryption round trip, including a payload longer than one AES block.
+  {
+    const phone = device();
+    const message = JSON.stringify({ title: "Period expected soon", body: "x".repeat(300) });
+    const body = push.encrypt(message, phone.p256dh, phone.authText);
+    assert.equal(body.readUInt32BE(16), 4096);
+    assert.equal(decrypt(body, phone.receiver, phone.auth), message);
+  }
+
+  // Reminder rules: regular 28-day cycles with the last one starting 1 Oct,
+  // so the next is expected 29 Oct.
+  {
+    const days = logPeriods(["2026-07-09", "2026-08-06", "2026-09-03", "2026-10-01"]);
+    const at = today => push.dueReminder(cycle.summarize(days, today), 2);
+    assert.equal(at("2026-10-26"), null);
+    assert.equal(at("2026-10-27").kind, "soon");
+    assert.match(at("2026-10-27").body, /in about 2 days, around Thu 29 Oct/);
+    assert.match(at("2026-10-28").body, /tomorrow/);
+    assert.equal(at("2026-10-29"), null, "due today is neither soon nor late");
+    assert.equal(at("2026-10-30").kind, "late");
+    assert.match(at("2026-10-30").body, /expected on Thu 29 Oct/);
+    assert.equal(at("2026-10-30").cycle, "2026-10-01");
+    assert.equal(push.dueReminder(cycle.summarize(days, "2026-10-27"), 1), null, "respects remind days");
+    assert.equal(push.dueReminder(cycle.summarize({}, "2026-10-27"), 2), null);
+    assert.equal(push.dueReminder(cycle.summarize(days, "2026-10-03"), 7), null, "nothing during a period");
+  }
+
+  // End to end: app.py creates the schema, `daily` sends one encrypted push
+  // to a fake push service, and a second run the same day sends nothing.
+  {
+    const dir = fs.mkdtempSync(path.join(os.tmpdir(), "flowtrack-push-"));
+    const database = path.join(dir, "flowtrack.sqlite3");
+    execFileSync(process.env.PYTHON || "python3", ["-c", `import sys; sys.path.insert(0, ${JSON.stringify(path.join(__dirname, ".."))}); import app; app.Store(${JSON.stringify(database)}).initialize()`]);
+
+    const received = [];
+    const server = http.createServer((request, response) => {
+      const chunks = [];
+      request.on("data", chunk => chunks.push(chunk));
+      request.on("end", () => {
+        received.push({ url: request.url, headers: request.headers, body: Buffer.concat(chunks) });
+        response.writeHead(request.url.endsWith("/gone") ? 410 : 201).end();
+      });
+    });
+    await new Promise(resolve => server.listen(0, "127.0.0.1", resolve));
+    const origin = `http://127.0.0.1:${server.address().port}`;
+
+    const { publicKey } = await push.main(["init", "--database", database]);
+    assert.equal(b64url.decode(publicKey).length, 65);
+    assert.equal((await push.main(["init", "--database", database])).publicKey, publicKey, "keys are stable");
+
+    const phone = device();
+    const db = new DatabaseSync(database);
+    const subscribe = db.prepare("INSERT INTO push_subscriptions (endpoint, p256dh, auth, user, created_at) VALUES (?, ?, ?, 'kayla', 'now')");
+    subscribe.run(`${origin}/push/phone`, phone.p256dh, phone.authText);
+    subscribe.run(`${origin}/push/gone`, phone.p256dh, phone.authText);
+    const log = db.prepare("INSERT INTO days (day, flow, symptoms, updated_at) VALUES (?, 'medium', '[]', 'now')");
+    for (const day of Object.keys(logPeriods(["2026-08-06", "2026-09-03", "2026-10-01"]))) log.run(day);
+
+    const args = ["daily", "--database", database, "--contact", "https://flowtrack.example.org", "--today", "2026-10-27"];
+    const first = await push.main(args);
+    assert.deepEqual({ due: first.due, sent: first.sent, removed: first.removed }, { due: "soon", sent: 1, removed: 1 });
+    assert.equal(db.prepare("SELECT COUNT(*) AS n FROM push_subscriptions").get().n, 1, "410 drops the subscription");
+
+    const delivered = received.find(request => request.url === "/push/phone");
+    assert.equal(delivered.headers["content-encoding"], "aes128gcm");
+    assert.equal(delivered.headers.ttl, "86400");
+    const claims = verifyVapid(delivered.headers.authorization, publicKey, origin);
+    assert.equal(claims.sub, "https://flowtrack.example.org");
+    const payload = JSON.parse(decrypt(delivered.body, phone.receiver, phone.auth));
+    assert.equal(payload.title, "Period expected soon");
+
+    const again = await push.main(args);
+    assert.equal(again.alreadySent, true);
+    assert.equal(received.length, 2, "no second send");
+
+    const test = await push.main(["test", "--database", database, "--contact", "https://flowtrack.example.org"]);
+    assert.equal(test.sent, 1);
+    assert.equal(JSON.parse(decrypt(received[2].body, phone.receiver, phone.auth)).tag, "test");
+
+    db.close();
+    server.close();
+    fs.rmSync(dir, { recursive: true });
+  }
+
+  console.log("push tests passed");
+})().catch(error => {
+  console.error(error);
+  process.exit(1);
+});