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

The calculation, step by step

Start by subtracting the birth year from the current year. If today's date hasn't reached the birth month and day yet this year, subtract one — you haven't had this year's birthday yet. That gives you the age in whole years.

For the leftover months and days, subtract the birth month/day from today's month/day the same way you'd do column subtraction by hand, borrowing a month (using that month's actual number of days) whenever the day count goes negative.

Why leap years and month lengths matter

Because months range from 28 to 31 days, the 'borrowing' step has to use the real length of the specific month being borrowed from, not a flat assumption. Someone born on January 31 being measured against March 15 needs to correctly account for February having only 28 or 29 days when figuring out the months/days breakdown.

People born on February 29 are a special case: in non-leap years, most conventions treat March 1 as their effective birthday for the purposes of turning a year older, since February 29 doesn't exist that year.

Total days lived

A separate, simpler number — total days lived — just takes the straight difference between the birth date and today, expressed in days, with no month/year breakdown involved. It's exact by construction since it works directly with real calendar dates, and it's a fun way to notice milestones (10,000 days, for instance) that don't line up with round birthday numbers.