My reminder is tiny and I can't enlarge it.

Configure Outlook to use its foreground Reminder window rather than a small notification banner; if the reminder comes from Windows Calendar, Windows 10 can enlarge or prolong notifications globally but does not provide a Calendar-specific large reminder window.

If you use new Outlook

1. Open Outlook.
2. Select Settings (gear icon) → General → Notifications.
3. Under Notify me about, turn Calendar on and expand that section.
4. Set Notification style to Reminder, not a banner-only style.
5. Enable the notification sound if desired.

The Reminder style uses a separate reminder window that opens over other programs. It also provides snooze and dismiss controls.^1^

There is no documented control for manually resizing this reminder window. If its contents remain too small, use the Windows scaling option below.

If you use classic Outlook

1. Open Outlook and select File → Options → Advanced.
2. Find the Reminders section.
3. Select Show reminders on top of other windows.
4. Optionally select Play reminder sound.
5. Select OK.

This keeps the Outlook reminder in front of the other windows you are using.^2^

The foreground option requires Outlook for Microsoft 365 Version 1804 (Build 9226.2114) or later. It is not available in Outlook 2021 or older.^1^

If the reminder comes from Windows Calendar

Windows Calendar notifications use the Windows notification system. To make them harder to miss:

1. Open Start → Settings → System → Notifications & actions.
2. Under Get notifications from these senders, select Calendar.
3. Turn on:
   • Show notification banners
   • Show notifications in action center
   • Play a sound when a notification arrives
4. Set Calendar’s notification priority as high as the available Windows 10 setting permits.^3^

To keep the banner visible longer:

1. Open Start → Settings → Ease of Access → Display.
2. Under Show notifications for, choose a longer duration.

Windows notifications normally disappear after five seconds, and this setting extends their display time system-wide.^4^

To enlarge the notification and other screen content:

1. Press Windows key + U.
2. On Display, use Make text bigger for text only, or select a larger value under Make everything bigger.
3. Select Apply. Some applications may require signing out and back in.^5^

This scaling change affects Windows generally; it is not limited to the Calendar reminder.

References

1. Classic Outlook(#tab/classic-outlook)
2. Advanced options in classic Outlook for Windows | Microsoft Support
3. Windows 10(#tab/windows-10)
4. Windows 10(#tab/windows-10)
5. Windows 10(#tab/windows-10)