Age calculator
Age is counted in whole calendar years, then whole months, then the remaining days. Someone born on 15 May 1990 is 36 years, 3 months and 8 days old on 23 August 2026. The day before a birthday you are still the previous age: the year only completes on the day itself.
How to work out an age
Month arithmetic is where these calculators disagree with each other. From 31 January to 1 March is one month and one day here, because adding a month to 31 January lands on 28 February; the last day that exists, and then one day gets you to 1 March. Any other rule produces an impossible date somewhere along the way.
Questions
A 29 February birthday falls back to 28 February in a common year for the "next birthday" figure, and returns to the 29th when the next leap year comes round.
Because it is a real elapsed count, not years times 365. Between 1 January 2024 and 1 January 2025 there are 366 days.
Yes. Change the second date to any day and you get the age as of that day, which is what forms and eligibility rules usually want.
You get the same span with a note saying the second date is in the future, so it reads as time remaining rather than age.