Guides / Dates

How to Calculate Your Exact Age in Years, Months and Days

Your age in years is easy to work out, but an exact age also includes months and days. The calculation needs one careful rule for borrowing from the previous month.

Count the years, months and days

Subtract the birth year from the current year, the birth month from the current month, and the birth day from the current day. If a result is negative, borrow: subtract one from the month or year above it, and add the length of the previous month to the day count.

A worked example

Someone born on 15 May 1990 checks their age on 26 October 2026. Years: 2026 minus 1990 is 36. Months: October minus May is 5. Days: 26 minus 15 is 11. No borrowing is needed, so the exact age is 36 years, 5 months and 11 days.

Days to the next birthday

Find the next birthday, which is this year's date if it has not passed yet, otherwise next year's. Then count the days from today to that date. For the example above, the next birthday is 15 May 2027, which is 201 days away.

Why the borrowing rule matters

If the checking date falls before the birthday in its month, a simple subtraction gives the wrong day count. Borrowing from the previous month fixes this. Months have different lengths, so the borrowed amount depends on which month it is.

Try it yourself

The Age Calculator does this for any date of birth and checking date, and it shows the total number of days lived too.