How to Calculate Age From Date of Birth

Working out someone’s age in whole years is easy. Getting the exact age in years, months and days is trickier, because months have different lengths and leap years add an extra day. Here’s the method, with examples.

The fast way

Enter the date of birth into the age calculator. It shows the exact age today, or on any date you choose, along with total days and the next birthday.

Calculating age by hand

Take a date of birth of 20 August 1994 and a current date of 5 March 2026.

1. Years: 2026 − 1994 = 32. But the birthday (20 August) hasn’t happened yet in 2026, so subtract one: 31 years. The last birthday was 20 August 2025.
2. Months: count whole months from 20 August 2025. 20 September, 20 October … 20 February 2026 is 6 months. 20 March hasn’t arrived, so it’s 6 months.
3. Days: from 20 February to 5 March 2026. February 2026 has 28 days, so that’s 8 days to the end of February plus 5 days: 13 days.

Result: 31 years, 6 months and 13 days.

The tricky cases

Birthdays on the 29th, 30th or 31st

If someone was born on 31 January, when do they turn one month old? February has no 31st. The common convention, used by our calculator, is the last day of the month: 28 February, or 29 February in a leap year.

Leap-day birthdays

People born on 29 February have a real birthday only every four years. In other years, the birthday is usually taken as 28 February. Some legal systems use 1 March instead, so for legal ages, such as the age of majority, check local rules.

Age in days, weeks or months

Total days is the exact number of days between the two dates, including every leap day. Divide by 7 for weeks. Total months is years × 12 plus the remaining months. Parents often use months for babies under two, which the calculator shows directly.

Age on a specific date

Many eligibility rules ask for age “as of” a cut-off date, such as 1 January of an exam year. Set “Age on this date” in the age calculator to that date. To count the days between any two dates instead, use the date difference calculator.