diff --git a/backend/app/plugins/sdk.py b/backend/app/plugins/sdk.py
index b74045c..61fb3a8 100644
--- a/backend/app/plugins/sdk.py
+++ b/backend/app/plugins/sdk.py
@@ -179,6 +179,12 @@ class PluginSdk:
         CalDAV/CardDAV/ICS. Returns status + headers + body."""
         return PluginHttp()
 
+    # --- notifications ------------------------------------------------------
+    @property
+    def push(self) -> PluginPush:
+        """Notifications on the user's devices (Web Push) — calendar reminders."""
+        return PluginPush(self.name)
+
     # --- secret vault -------------------------------------------------------
     @property
     def vault(self) -> PluginVault:
@@ -187,6 +193,39 @@ class PluginSdk:
         return PluginVault()
 
 
+class PluginPush:
+    """``sdk.push``: show a notification on every device where the user turned
+    notifications on (Settings → Accounts → Notifications)."""
+
+    def __init__(self, plugin: str) -> None:
+        self._plugin = plugin
+
+    async def notify(
+        self,
+        user_id: uuid.UUID,
+        *,
+        title: str,
+        body: str = "",
+        url: str = "/mail",
+        tag: str | None = None,
+        sticky: bool = False,
+    ) -> int:
+        """Send one notification; returns how many devices it went to. ``tag``
+        replaces an earlier notification with the same tag (it is prefixed with
+        the plugin's name); ``sticky`` keeps it on screen until dismissed."""
+        from app.push.service import deliver
+
+        payload: dict[str, object] = {
+            "type": f"plugin.{self._plugin}",
+            "title": title[:200],
+            "body": body[:500],
+            "url": url if url.startswith("/") else "/mail",
+            "tag": f"{self._plugin}-{tag}" if tag else self._plugin,
+            "sticky": sticky,
+        }
+        return await deliver(user_id, [payload])
+
+
 def sdk(name: str) -> PluginSdk:
     """Return the SDK facade bound to plugin ``name`` (SPEC §11)."""
     return PluginSdk(name)
diff --git a/backend/app/push/service.py b/backend/app/push/service.py
index f55aeb9..288d65e 100644
--- a/backend/app/push/service.py
+++ b/backend/app/push/service.py
@@ -200,6 +200,26 @@ async def notify(user_id: uuid.UUID, message_ids: list[uuid.UUID]) -> int:
     pushes were delivered to push services."""
     from app.db import session_scope
 
+    async with session_scope() as db:
+        if not await db.scalar(
+            select(PushSubscription.id).where(PushSubscription.user_id == user_id).limit(1)
+        ):
+            return 0
+        messages = await _news(db, user_id, message_ids)
+        if not messages:
+            return 0
+        payloads = _payloads(messages, await _unread(db, user_id))
+    return await deliver(user_id, payloads)
+
+
+async def deliver(user_id: uuid.UUID, payloads: list[dict[str, object]]) -> int:
+    """Push ``payloads`` to every device of the user that is still signed in
+    (for new mail, and for plugins: calendar reminders); returns how many were
+    handed to push services. Devices that are gone are forgotten."""
+    from app.db import session_scope
+
+    if not payloads:
+        return 0
     async with session_scope() as db:
         # Plain values: the rows expire when the key pair is first saved below.
         subs = [
@@ -210,10 +230,6 @@ async def notify(user_id: uuid.UUID, message_ids: list[uuid.UUID]) -> int:
         ]
         if not subs:
             return 0
-        messages = await _news(db, user_id, message_ids)
-        if not messages:
-            return 0
-        payloads = _payloads(messages, await _unread(db, user_id))
         key = await vapid(db)
         subject = _subject(await db.get(AppSettings, 1))
 
diff --git a/backend/tests/plugins/test_calendar_reminders.py b/backend/tests/plugins/test_calendar_reminders.py
new file mode 100644
index 0000000..da39d6c
--- /dev/null
+++ b/backend/tests/plugins/test_calendar_reminders.py
@@ -0,0 +1,130 @@
+"""Event reminders as notifications (calendar plugin, sdk.push): due reminders
+are sent once, repeating events remind on each occurrence, cancelled and
+declined ones stay quiet."""
+
+from __future__ import annotations
+
+import uuid
+from collections.abc import AsyncIterator
+from datetime import UTC, datetime, timedelta
+from typing import Any
+
+import httpx
+import pytest
+import pytest_asyncio
+from httpx import ASGITransport
+from sqlalchemy import delete, text
+from sqlalchemy.ext.asyncio import async_sessionmaker, create_async_engine
+from sqlalchemy.pool import NullPool
+from webmail_plugin_calendar import reminders  # type: ignore[import-not-found]
+
+from app.config import get_settings
+from app.identity.passwords import hash_password
+from app.identity.sessions import create_session
+from app.main import create_app
+from app.models import User
+from app.plugins.sdk import PluginPush
+
+CAL = "/api/plugins/calendar"
+# Far from any real event in the dev database.
+MON_9 = datetime(2031, 6, 2, 9, 0, tzinfo=UTC)  # a Monday
+
+
+@pytest_asyncio.fixture
+async def ctx(
+    monkeypatch: pytest.MonkeyPatch,
+) -> AsyncIterator[tuple[httpx.AsyncClient, uuid.UUID, list[dict[str, Any]], Any]]:
+    sent: list[dict[str, Any]] = []
+
+    async def fake_notify(self: PluginPush, user_id: uuid.UUID, **kw: Any) -> int:
+        sent.append({"user_id": user_id, **kw})
+        return 1
+
+    monkeypatch.setattr(PluginPush, "notify", fake_notify)
+    engine = create_async_engine(get_settings().database_url, poolclass=NullPool)
+    sm = async_sessionmaker(engine, expire_on_commit=False)
+    async with sm() as s:
+        user = User(
+            handle=f"rem{uuid.uuid4().hex[:8]}@test.local", password_hash=hash_password("pw")
+        )
+        s.add(user)
+        await s.commit()
+    token = await create_session(user.id, "pytest")
+    client = httpx.AsyncClient(
+        transport=ASGITransport(app=create_app()),
+        base_url="http://testserver",
+        cookies={"session": token, "csrf": "c"},
+        headers={"X-CSRF": "c"},
+    )
+    try:
+        yield client, user.id, sent, sm
+    finally:
+        await client.aclose()
+        async with sm() as s:
+            await s.execute(
+                text("DELETE FROM plg_calendar_calendars WHERE user_id = :u"), {"u": str(user.id)}
+            )
+            await s.execute(text("DELETE FROM plugin_kv WHERE user_id = :u"), {"u": str(user.id)})
+            await s.execute(delete(User).where(User.id == user.id))
+            await s.commit()
+        await engine.dispose()
+
+
+async def _event(client: httpx.AsyncClient, **fields: Any) -> str:
+    cal = (await client.get(f"{CAL}/calendars")).json()[0]["id"]
+    r = await client.post(f"{CAL}/events", json={"calendar_id": cal, **fields})
+    assert r.status_code == 200, r.text
+    return str(r.json()["id"])
+
+
+async def test_due_reminders_are_sent_once(ctx) -> None:  # type: ignore[no-untyped-def]
+    client, user_id, sent, sm = ctx
+    await _event(
+        client,
+        summary="Dentist",
+        location="Main St 4",
+        dtstart=MON_9.isoformat(),
+        dtend=(MON_9 + timedelta(hours=1)).isoformat(),
+        reminders=[10, 60],
+    )
+    called_off = await _event(
+        client, summary="Called off", dtstart=MON_9.isoformat(), reminders=[10]
+    )
+    async with sm() as db:  # cancelled by its organizer: never reminds
+        await db.execute(
+            text("UPDATE plg_calendar_events SET status = 'cancelled' WHERE id = :id"),
+            {"id": called_off},
+        )
+        await db.commit()
+
+    async def run(at: datetime) -> int:
+        return await reminders.reminder_job({}, now=at, only_user=user_id)
+
+    assert await run(MON_9 - timedelta(minutes=61)) == 0  # nothing due yet
+    assert await run(MON_9 - timedelta(minutes=60)) == 1  # the 1-hour reminder
+    assert sent[-1]["title"] == "Dentist"
+    assert sent[-1]["body"] == "In 1 hour, 09:00 · Main St 4"
+    assert sent[-1]["url"] == "/p/calendar?date=2031-06-02" and sent[-1]["sticky"] is True
+    assert await run(MON_9 - timedelta(minutes=59)) == 0  # not again
+    # The worker was down when the 10-minute reminder came due: sent late, once.
+    assert await run(MON_9 - timedelta(minutes=4)) == 1
+    assert sent[-1]["body"] == "In 10 minutes, 09:00 · Main St 4"
+    assert await run(MON_9 - timedelta(minutes=3)) == 0
+    assert len(sent) == 2
+
+
+async def test_repeating_events_remind_on_each_occurrence(ctx) -> None:  # type: ignore[no-untyped-def]
+    client, user_id, sent, _ = ctx
+    await _event(
+        client,
+        summary="Weekly sync",
+        dtstart=MON_9.isoformat(),
+        dtend=(MON_9 + timedelta(minutes=30)).isoformat(),
+        rrule="FREQ=WEEKLY;BYDAY=MO",
+        reminders=[15],
+    )
+    for week in range(3):
+        at = MON_9 + timedelta(weeks=week) - timedelta(minutes=15)
+        assert await reminders.reminder_job({}, now=at, only_user=user_id) == 1
+    tags = {s["tag"] for s in sent}
+    assert len(sent) == 3 and len(tags) == 3  # one notification per occurrence
diff --git a/frontend/public/sw.js b/frontend/public/sw.js
index fb1f3dd..dcd6387 100644
--- a/frontend/public/sw.js
+++ b/frontend/public/sw.js
@@ -501,11 +501,13 @@ self.addEventListener("activate", (event) => {
   );
 });
 
-// ---- notifications about new mail ---------------------------------------------------
+// ---- notifications: new mail, calendar reminders ------------------------------------
 //
 // The server (app/push/service.py) sends { type: "mail", title, body, tag, url,
 // unread } encrypted to this browser. One notification per conversation (`tag`),
 // replaced when more arrives in it; the app icon's badge shows unread Inbox mail.
+// A plugin (sdk.push) sends { type: "plugin.<name>", title, body, tag, url,
+// sticky } — a calendar reminder.
 
 /** A window of the app the user is looking at right now. */
 async function lookingAtApp() {
@@ -517,16 +519,21 @@ async function showMail(data) {
   if (typeof data.unread === "number" && self.navigator.setAppBadge) {
     await (data.unread ? self.navigator.setAppBadge(data.unread) : self.navigator.clearAppBadge()).catch(() => {});
   }
-  // The app is open in front of the user: the new mail is already on screen.
-  // Not on Apple's push service, which withdraws permission from a site whose
+  // New mail while the app is open in front of the user: it is already on
+  // screen. (Other notifications — a calendar reminder — show regardless.) Not
+  // on Apple's push service, which withdraws permission from a site whose
   // pushes show nothing.
-  const sub = await self.registration.pushManager.getSubscription();
-  const apple = Boolean(sub?.endpoint.includes(".push.apple.com"));
-  if (!apple && (await lookingAtApp())) return;
+  if (!data.type || data.type === "mail") {
+    const sub = await self.registration.pushManager.getSubscription();
+    const apple = Boolean(sub?.endpoint.includes(".push.apple.com"));
+    if (!apple && (await lookingAtApp())) return;
+  }
   await self.registration.showNotification(data.title || "New mail", {
     body: data.body || "",
     tag: data.tag || "new-mail",
     renotify: true,
+    // A reminder stays until dismissed (where the platform allows it).
+    requireInteraction: Boolean(data.sticky),
     icon: "/icon-192.png",
     badge: "/badge-96.png",
     timestamp: Date.now(),
diff --git a/plugins/webmail_plugin_calendar/webmail_plugin_calendar/reminders.py b/plugins/webmail_plugin_calendar/webmail_plugin_calendar/reminders.py
new file mode 100644
index 0000000..ff8792a
--- /dev/null
+++ b/plugins/webmail_plugin_calendar/webmail_plugin_calendar/reminders.py
@@ -0,0 +1,171 @@
+"""Event reminders as notifications on the user's devices (Web Push).
+
+Every minute, the events with reminders that fall due are found — repeating
+events expanded and moved occurrences honoured by the same code the calendar
+view uses (queries.expand_range) — and each due reminder is pushed through
+``sdk.push`` to every device where the user turned notifications on. A
+reminder is sent once (remembered in the plugin's KV store); one that came due
+while the worker was down is still sent within CATCH_UP. Cancelled events and
+invitations the user declined stay quiet.
+"""
+
+from __future__ import annotations
+
+import logging
+import uuid
+from collections import defaultdict
+from datetime import UTC, datetime, timedelta
+from typing import Any
+from zoneinfo import ZoneInfo, ZoneInfoNotFoundError
+
+from sqlalchemy import text
+
+from app.plugins.sdk import sdk
+from webmail_plugin_calendar.queries import expand_range
+
+logger = logging.getLogger("plg.calendar")
+_SDK = sdk("calendar")
+
+CATCH_UP = timedelta(minutes=10)  # a reminder due this long ago is still sent
+MAX_LEAD = timedelta(days=8)  # reminders this far ahead of an event are looked for
+_SENT_KEY = "reminders_sent"  # KV: {"<event>|<start>|<minutes>": due-time ISO}
+
+_COLUMNS = (
+    "e.id, e.user_id, e.calendar_id, e.ical_uid, e.summary, e.description, e.location, "
+    "e.dtstart, e.dtend, e.all_day, e.tz, e.rrule, e.reminders, e.exdates, "
+    "e.recurrence_id, e.status, e.my_partstat, e.origin_message_id, e.show_as, "
+    "e.conference_url, e.attendees, e.organizer, COALESCE(e.color, c.color) AS color"
+)
+
+
+def _when(start: datetime, minutes_before: int, all_day: bool, tz: str, hour12: bool) -> str:
+    """The notification's line under the title: when the event starts."""
+    if all_day:  # date-anchored at UTC midnight
+        return f"All day, {start.astimezone(UTC).strftime('%a %d %b')}"
+    local = start.astimezone(_zone(tz))
+    clock = local.strftime("%I:%M %p").lstrip("0") if hour12 else local.strftime("%H:%M")
+    if minutes_before <= 0:
+        return f"Now, {clock}"
+    if minutes_before < 60:
+        return f"In {minutes_before} minutes, {clock}"
+    if minutes_before < 24 * 60:
+        hours = minutes_before // 60
+        return f"In {hours} hour{'s' if hours > 1 else ''}, {clock}"
+    days = minutes_before // (24 * 60)
+    day = "Tomorrow" if days == 1 else local.strftime("%a %d %b")
+    return f"{day}, {clock}"
+
+
+def due(
+    instances: list[dict[str, Any]], lo: datetime, now: datetime
+) -> list[tuple[dict[str, Any], int]]:
+    """The (instance, minutes before) reminders falling due in ``(lo, now]``."""
+    out = []
+    for inst in instances:
+        if inst["status"] == "cancelled" or inst.get("my_partstat") == "declined":
+            continue
+        start = datetime.fromisoformat(inst["start"])
+        for minutes in sorted(set(inst.get("reminders") or [])):
+            fire = start - timedelta(minutes=minutes)
+            if lo < fire <= now:
+                out.append((inst, minutes))
+    return out
+
+
+async def _notify_user(
+    user_id: uuid.UUID, hits: list[tuple[dict[str, Any], int]], now: datetime
+) -> int:
+    kv = _SDK.kv(user_id)
+    sent: dict[str, str] = dict(await kv.get(_SENT_KEY, {}) or {})
+    settings = await _SDK.accounts.settings_of(user_id)
+    hour12 = str(settings.get("time_format", "24")) == "12"
+    tz = str(settings.get("tz") or "UTC")
+    delivered = 0
+    for inst, minutes in hits:
+        key = f"{inst['id']}|{inst['start']}|{minutes}"
+        if key in sent:
+            continue
+        start = datetime.fromisoformat(inst["start"])
+        body = _when(start, minutes, inst["all_day"], tz, hour12)
+        if inst.get("location"):
+            body += f" · {inst['location']}"
+        title = inst["summary"] or "(no title)"
+        delivered += await _SDK.push.notify(
+            user_id,
+            title=title,
+            body=body,
+            url=f"/p/calendar?date={_day(start, inst['all_day'], tz)}",
+            # One notification per occurrence: a later reminder replaces an earlier one.
+            tag=f"event-{inst['id']}-{inst['start']}",
+            sticky=True,
+        )
+        sent[key] = (start - timedelta(minutes=minutes)).isoformat()
+    # Forget reminders of events long past.
+    horizon = now - timedelta(days=2)
+    sent = {k: v for k, v in sent.items() if datetime.fromisoformat(v) > horizon}
+    await kv.set(_SENT_KEY, sent)
+    return delivered
+
+
+def _day(start: datetime, all_day: bool, tz: str) -> str:
+    """The event's day (YYYY-MM-DD) as the user's calendar shows it."""
+    return start.astimezone(UTC if all_day else _zone(tz)).date().isoformat()
+
+
+def _zone(tz: str) -> ZoneInfo:
+    try:
+        return ZoneInfo(tz or "UTC")
+    except (ZoneInfoNotFoundError, ValueError):
+        return ZoneInfo("UTC")
+
+
+async def reminder_job(
+    ctx: dict[str, Any], now: datetime | None = None, only_user: uuid.UUID | None = None
+) -> int:
+    """Cron job (every minute): push the reminders that fell due. ``now`` and
+    ``only_user`` are for tests."""
+    now = now or datetime.now(UTC)
+    lo = now - CATCH_UP
+    hi = now + MAX_LEAD
+    async with _SDK.public_session() as pub:
+        rows = (
+            (
+                await pub.execute(
+                    text(
+                        f"SELECT {_COLUMNS} FROM plg_calendar_events e "
+                        "JOIN plg_calendar_calendars c ON c.id = e.calendar_id "
+                        "WHERE e.dav_deleted = false "
+                        + ("AND e.user_id = :uid " if only_user else "")
+                        + "AND ("
+                        # events with reminders: repeating ones, or ones starting soon
+                        " (e.recurrence_id IS NULL AND e.reminders <> '{}' "
+                        "  AND (e.rrule IS NOT NULL OR e.dtstart BETWEEN :lo AND :hi))"
+                        # moved / cancelled occurrences of repeating events
+                        " OR (e.recurrence_id IS NOT NULL "
+                        "  AND (e.dtstart BETWEEN :lo AND :hi "
+                        "       OR e.recurrence_id BETWEEN :lo AND :hi)))"
+                    ),
+                    {"lo": lo, "hi": hi, **({"uid": only_user} if only_user else {})},
+                )
+            )
+            .mappings()
+            .all()
+        )
+    by_user: dict[uuid.UUID, list[Any]] = defaultdict(list)
+    for r in rows:
+        by_user[uuid.UUID(str(r["user_id"]))].append(r)
+
+    total = 0
+    for user_id, user_rows in by_user.items():
+        base = [r for r in user_rows if r["recurrence_id"] is None]
+        if not base:
+            continue
+        overrides = [r for r in user_rows if r["recurrence_id"] is not None]
+        hits = due(expand_range(base, overrides, lo, hi), lo, now)
+        if not hits:
+            continue
+        try:
+            total += await _notify_user(user_id, hits, now)
+        except Exception:  # noqa: BLE001 - one user's trouble must not stop the rest
+            logger.warning("calendar reminders failed for user %s", user_id, exc_info=True)
+    return total
diff --git a/plugins/webmail_plugin_calendar/webmail_plugin_calendar/ui/page.js b/plugins/webmail_plugin_calendar/webmail_plugin_calendar/ui/page.js
index a47f67a..5e2d28e 100644
--- a/plugins/webmail_plugin_calendar/webmail_plugin_calendar/ui/page.js
+++ b/plugins/webmail_plugin_calendar/webmail_plugin_calendar/ui/page.js
@@ -1850,6 +1850,18 @@ export default function mount(el, ctx, props) {
   (async () => {
     await loadChrome();
     await loadCalendars();
+    // Deep link (a reminder notification): /p/calendar?date=YYYY-MM-DD opens that
+    // day, then strips the param so refresh is clean.
+    try {
+      const day = new URLSearchParams(window.location.search).get("date");
+      if (!state.embed && day && /^\d{4}-\d{2}-\d{2}$/.test(day)) {
+        const [y, m, d] = day.split("-").map(Number);
+        state.anchor = startOfDay(new Date(y, m - 1, d));
+        state.mini = startOfMonth(state.anchor);
+        state.view = "day";
+        window.history.replaceState({}, "", window.location.pathname);
+      }
+    } catch { /* ignore */ }
     await loadEvents();
     render();
     // Embed mode ("Invite all to new event" from Mail's People tab): open a new-event