How to Calculate Age From a Date of Birth
3 min read
Calculating an age sounds like simple subtraction, but the month and day matter - someone born in December is not the same age as someone born in January of the same year. Here is how to get it exactly right.
Here is how to calculate age from a date of birth.
Step by step
- 1Subtract the birth year from the current year
This gives a rough age. Born in 1990, today in 2026, that is 36 - but only if the birthday has already happened this year.
- 2Check whether the birthday has passed
If today's month and day are before the birth month and day, subtract one, because the birthday has not occurred yet this year.
- 3Get months and days for an exact age
Count the full months since the last birthday, then the days since that month mark, to express age as years, months, and days.
- 4Use the calculator
Enter the birth date in the Age Calculator to get the exact age in years, months, and days, including across leap years.
Tips
- Leap years (February 29) are handled automatically by the calculator - a tricky case to do by hand.
- The same method finds the time between any two dates, not just from birth to today.
- For legal age thresholds, the day itself counts - you turn the age on your birthday, not the day after.
Frequently asked questions
How do I calculate someone's age?
Subtract the birth year from the current year, then subtract one if this year's birthday has not happened yet (today's month/day is before the birth month/day).
How do I get age in months and days too?
After the years, count the whole months since the last birthday and the leftover days. The age calculator does this precisely, including leap years.
Does it account for leap years?
Yes. The calculator counts actual calendar days, so February 29 birthdays and leap years are handled correctly.