How to Fix Phone Calendar Reminders That Are Not Working

Published 2026-10-16 · Marion Phone Repair

Missing a calendar reminder means missing a meeting, an appointment, a deadline, or a pickup time. When your phone stops alerting you to calendar events, the problem is almost never the calendar app itself — it is usually a notification setting, a sync issue, or a power-saving feature that is silencing the alerts before they reach you.

Check notification permissions for the calendar app

The most common reason calendar reminders stop is that notifications for the calendar app were accidentally turned off. A single accidental tap on a "mute" prompt or a software update resetting permissions is enough.

iPhone

Open Settings, then Notifications
Scroll down and tap Calendar
Make sure Allow Notifications is toggled on
Under Alerts, enable Lock Screen, Notification Center, and Banners — all three should be on if you want to see reminders regardless of what you are doing when they fire
Make sure Sounds is toggled on. Without this, the reminder appears silently and you only see it if you happen to look at your phone
Check the Banner Style — set it to Persistent if you want the notification to stay on screen until you dismiss it, rather than disappearing after a few seconds

Android

Open Settings, Apps (or Apps and notifications)
Find your calendar app (Google Calendar, Samsung Calendar, or whichever you use) and tap it
Tap Notifications
Make sure notifications are turned on for the app. Android often breaks calendar notifications into categories — look for categories like Event reminders, Upcoming events, or Alerts. Make sure the reminder-specific category is enabled, not just the general app notification
Check that the notification importance or priority is set to High or Default, not Silent or Low. A silent notification delivers but makes no sound and may not show on the lock screen

Check Do Not Disturb and Focus modes

Do Not Disturb (DND) and Focus modes silence notifications, including calendar reminders, unless you specifically allow them through.

iPhone

Open Settings, Focus. Check each Focus mode you use (Do Not Disturb, Work, Sleep, etc.). Under each mode, look at Allowed Notifications — make sure the Calendar app is in the allowed list, or that Time Sensitive Notifications is enabled (calendar reminders are classified as time-sensitive)
Check if a Focus mode is currently active — look for the Focus icon (crescent moon for DND, or the custom icon for other modes) in the status bar or Control Center. If a Focus mode is on and Calendar is not in its allow list, that is why you are missing reminders

Android

Open Settings, Sound (or Notifications), Do Not Disturb. Check the Exceptions or Allowed during DND section. Look for an option to allow reminders or calendar notifications through DND
On Samsung phones, this is under Settings, Notifications, Do not disturb, Allowed during Do not disturb. Make sure Reminders is toggled on
Some Android phones have a Bedtime mode or Sleep mode that silences notifications on a schedule — check if this is active and whether calendar apps are excluded

Verify the calendar account is syncing

If you use a cloud calendar (Google Calendar, iCloud Calendar, Outlook, Exchange), reminders only work if the calendar is actively syncing to your phone. A sync problem means the event may be on the server but not on your phone, so no local reminder fires.

iPhone

Open Settings, Calendar, Accounts
Tap each calendar account (iCloud, Gmail, Exchange, etc.) and make sure Calendars is toggled on
Go back to Settings, Calendar, and check Default Calendar — make sure it is set to the account you actually use. If the default is set to a local "On My iPhone" calendar that does not sync, events you create may not appear on your other devices or may not trigger cloud-based reminders

Android

Open Settings, Accounts, then tap your Google account (or whichever account hosts your calendar)
Tap Account sync and make sure Calendar is toggled on
If Calendar sync was off, toggle it on and tap the three-dot menu to Sync now
Open Google Calendar, tap the hamburger menu (three lines), and check that the specific calendars you want reminders from are checked. Each Google account can have multiple calendars (primary, holidays, shared calendars, etc.) — unchecked calendars do not show events or fire reminders

Check the event's reminder setting

Individual calendar events have their own reminder settings that override the app's default. An event with no reminder set will not trigger an alert even if everything else is working correctly.

Open the calendar event that you missed and check its reminder or alert field. If it says None, add a reminder (10 minutes before, 30 minutes before, or whatever time you need)
Check your calendar app's default reminder setting so new events automatically include a reminder:
- iPhone: Settings, Calendar, Default Alert Times. Set default alerts for Events, All-Day Events, and Birthdays
- Google Calendar (web): Settings, Event settings, Default notifications. Set a default notification time. This applies to new events — it does not retroactively add reminders to existing events

Check battery optimization settings

Android's battery optimization (also called app sleep, deep sleep, or adaptive battery) can prevent calendar apps from running in the background, which means they cannot check for upcoming events and fire reminders on time.

Stock Android

Open Settings, Apps, find your calendar app, tap Battery
Set it to Unrestricted (not Optimized or Restricted). Unrestricted allows the app to run in the background without limits

Samsung

Open Settings, Battery and device care, Battery, Background usage limits
Check the Sleeping apps and Deep sleeping apps lists. If your calendar app is in either list, remove it by tapping the list and unchecking the app. Apps in these lists are aggressively suspended and may not fire notifications on time

Other Android brands

Xiaomi, Huawei, OnePlus, and other manufacturers have their own aggressive battery management that frequently kills calendar apps. Search your phone's Settings for "battery optimization" or "app launch" and make sure your calendar app is set to manual management with auto-launch and background activity allowed. These manufacturer-specific battery features are the single most common cause of missed calendar reminders on Android.

Restart the phone

If all settings look correct but reminders still are not firing, restart the phone. A restart clears any temporary software glitches that may be preventing the notification system from working properly. Calendar reminder delivery depends on several background services — the calendar sync service, the notification manager, and the alarm scheduler — and any of these can stall without producing an obvious error. A restart resets all of them.

Reinstall or clear the calendar app cache

If reminders are still not working after checking every setting above:

Android: Go to Settings, Apps, your calendar app, Storage, and tap Clear cache. If that does not help, tap Clear data (this removes the app's local data but your events are safe on the server and will re-sync). After clearing data, open the app and let it sync
iPhone: Delete the third-party calendar app and reinstall it from the App Store. For the built-in Calendar app (which cannot be deleted), toggle Calendars off for all accounts in Settings, Calendar, Accounts, wait 30 seconds, then toggle them back on to force a fresh sync

Calendar reminder help in Marion

If your phone calendar reminders are not working and the steps above have not resolved the issue, Marion Phone Repair can check whether the problem is a software configuration issue, a system-level bug, or a deeper problem with your phone's notification system.