How to Calculate Your Age From a Date of Birth
Learning how to calculate your age from a date of birth sounds easy — until months and leap years get involved. Here's the clean way to do it by hand, the traps to avoid, and the fastest way to get an exact answer.
The quick method
- Subtract the birth year from the current year. That's your rough age.
- Check the birthday. If this year's birthday hasn't happened yet, subtract one. Done — that's your age in whole years.
Example: born 1990, today's year 2026 → 36. If the 1990 birthday is later this year, you're still 35 until it arrives.
Getting years, months, and days
For a precise age, work down the units in order:
- Years: full years between the dates.
- Months: whole months since the last birthday.
- Days: remaining days since the last whole month.
The tricky part is "borrowing" when the day or month goes negative — for instance, from Jan 31 to Mar 1, the day count needs care because February is short. Leap years add a 29th day every four years, which shifts the totals slightly. Doing this perfectly by hand is fiddly, which is exactly why a calculator is handy.
Let the calculator do it
Our Age Difference Calculator handles all of it — months of different lengths, leap years, any order of dates — and returns the exact gap in years, months, days, and total days. Enter a birth date and today's date to get your precise age, or two birth dates to compare two people.