How to Calculate Your Exact Age in Years, Months and Days
Working out your age in years is easy: subtract the birth year from this year, then take one off if your birthday has not arrived yet. Getting it exact, in years, months and days, takes a few more steps. Here is the method, plus the special cases that cause mistakes.
The step-by-step method
Write the two dates as day, month and year, with today's date on top and the date of birth below. Subtract in this order: days, then months, then years.
- Subtract the days. If today's day is smaller than the birth day, borrow the number of days in the previous month and reduce the month by one.
- Subtract the months. If today's month is smaller than the birth month, borrow 12 months and reduce the year by one.
- Subtract the years.
Example 1: a simple case
Born on 15 August 1995. Today is 23 October 2026.
- Days: 23 − 15 = 8
- Months: 10 − 8 = 2
- Years: 2026 − 1995 = 31
Age: 31 years, 2 months and 8 days.
Example 2: borrowing days and months
Born on 28 December 2000. Today is 10 March 2026.
- Days: 10 is smaller than 28, so borrow the days of the previous month. The month before March is February 2026, which has 28 days. So 10 + 28 − 28 = 10, and the month count reduces by one (March becomes month 2).
- Months: 2 is smaller than 12, so borrow 12 months. 2 + 12 − 12 = 2, and the year count reduces by one.
- Years: 2026 − 1 − 2000 = 25
Age: 25 years, 2 months and 10 days. You can check this: from 28 December 2025 to 28 February 2026 is two months, and from 28 February to 10 March 2026 is 10 days.
Leap years and 29 February birthdays
A leap year has 366 days, with an extra day, 29 February, added to the month of February. A year is a leap year if it is divisible by 4, except century years, which must be divisible by 400. So 2000 was a leap year and 1900 was not.
People born on 29 February have their actual birthday only every four years. In non-leap years, most places treat the birthday as either 28 February or 1 March, depending on local rules. Many legal systems count the person as turning a year older on 1 March in a non-leap year, while some use 28 February, so check which rule applies to the document you are filling in. Our Age Calculator handles leap-day birthdays and shows the result clearly.
Counting total days and weeks
Sometimes you need your age in days, for example to see how many days old a baby is. Count the days from the birth date to today. Roughly, one year is 365.25 days on average, so a person aged 31 is about 31 × 365.25 = 11,323 days old. For an exact count, use a date calculator, because the number depends on which leap days fell in between.
Where an exact age matters
- Exams and jobs: eligibility often depends on your age on a fixed date, such as the first of January or the last day of applications. Use that date, not today's date.
- School admission: many schools require a child to reach a certain age by a set cut-off date.
- Insurance and pensions: premiums and benefits change at specific ages, and some count age at the nearest birthday rather than the last one.
- Medical care: doctors and vaccination schedules for babies count age in weeks and months.
Common mistakes
- Subtracting years only and forgetting that the birthday may not have happened yet this year.
- Using 30 days for every month when borrowing. Use the real length of the previous month.
- Forgetting that February has 29 days in a leap year.
- Calculating to today when a form asks for your age on a different date.
To check any result, enter your birth date and the date you need into the Age Calculator. It also shows how many days remain until your next birthday.