What this birthday countdown calculates
The result finds the next occurrence of the entered month and day on or after the reference date. It reports the exact whole-day interval, birthday date, weekday and age reached on that birthday.
February 29 birthdays
In a non-leap year this calculator uses February 28 as the observed countdown date. This is a transparent calculator convention, not a legal rule; official treatment can differ by jurisdiction.
Today versus the next annual birthday
If the birthday is today, the countdown returns zero days. Once the reference date moves past the birthday, the result advances to the following year.