On iOS, the information saved to your contacts is synced to Calendar. If you have a contact synced from Facebook, their birthday will appear in the Calendar app. You can add other calendars to the Calendar app and all events, birthdays, and anniversaries will sync to it. You can also add events to the app and get reminders for them. iOS is smart enough to pick events from Mail invites and add them automatically to Calendar. Surprisingly, you cannot add an annual event, such as an anniversary to Calendar. You can sync information from other apps that store this type of information but you can’t just add it directly. There are workarounds to this limitation though.
Add Annual Google Calendar Event
The Calendar app on iOS doesn’t let you add annual events but Google Calendar does. You can add an annual event in Google Calendar, and then sync Google Calendar to the Calendar app on iOS.
To create an annual event in Google Calendar, visit Google Calendar and click inside the time slot on the day of the annual event you want to add. Fill in the basic detail i.e., the name, and then click the More Options button.
On the More Options screen, you will see a dropdown labeled ‘Do not repeat’. From this dropdown, select the annual event option. Remove any other reminders that you don’t want associated with this event.
Next, open the Settings app on your iPhone or iPad. Go to Accounts & Passwords, and tap Add Account. Select Google on the next screen, and sign in with your Google account. Sync only the Calendar, if you don’t want to sync email and contacts.
Visit the Calendar app, and your annual event will appear on the date you added it on.
Add Fake Contact
If the Google Calendar route seems a bit too long and tedious to set up, you can go with an easier and quicker hack; create a fake contact. You can name the contact anything you want but it’s best to give it the same name as the annual event you want to add. Once you’ve added the contact, enter a birthday for it. That birthday should be the date of the anniversary or annual event you want to add.
This workaround has an obvious shortcoming; you will have lots of fake contacts that are added just for the sake of adding annual events. If you only need to add one anniversary to Calendar, you can use this second hack but if you have to add more then consider using the Google Calendar annual event method.