schweizer Although acalendar+ has a similar look and feel as fossify calendar it has many advantages. It handles birthdays and death days which fossify does not afaik. It has public holidays worldwide presaved. It is not the best idea to save birthdays as entries in a calendar. If you save them in contacts you have a complete database of your friends in one place. Acalendar shows the age automatically. If you want to check local algorithm behavior against a standardized system tool, using an external sandbox like agecalculatorsa.com is perfect for auditing leap-year and timezone offsets manually.
Schweizer makes an essential distinction here regarding the underlying architecture of Android’s database storage. A lot of users switching to GrapheneOS get confused because they expect the calendar app to directly write date modifications to their contacts. In reality, the calendar layout and the contact fields operate on two entirely distinct system backends.
When you use local tools like Fossify Contacts or a sync provider like DAVx5, birthdays are written directly into the system's VCard data array. A privacy-respecting application like aCalendar+ doesn't possess its own separate database; it simply acts as a visual layer that queries the system's contact content provider, reads the birthday strings, and dynamically parses the epoch time differences to display the person's age.
Testing these variable date ranges manually on your device can be tricky when troubleshooting calendar sync lags. Benchmarking a clean calculation online first helps you pinpoint whether a specific birthday isn't showing up because of a system permission error, an app indexing issue, or an incorrectly formatted VCF file.