Age Calculator

It compares your date of birth to today's date using calendar-aware arithmetic - counting whole years, then whole months, then whole days - rather than an approximation like dividing total days by 365, which would drift inaccurate over time due to leap years and months of different lengths. The result is always calculated against the current date, so it updates automatically every time you use the calculator.

The calculator rejects it - a date of birth cannot be later than today, since that would describe someone who has not been born yet. You will need to correct the date before a result can be calculated.

In a leap year, February 29 works exactly like any other birthday. In a non-leap year, since February 29 does not exist on the calendar that year, this calculator treats the birthday as falling on February 28 for the purpose of calculating the next birthday and the countdown to it - a deliberate, documented choice, not a silent default.

It is the number of full calendar days between today and the next date your birthday falls on, counting forward to next year if this year's birthday has already passed. If today is your birthday, the calculator shows a "Happy Birthday" message instead of a countdown, since the countdown would otherwise read as zero.