Age in years, months and days:
an exact age from any date of birth

How to calculate age from date of birth

Your age on a given day is the time that has passed since you were born, expressed as completed years, then the months and days left over. A person born on 23 July 1994 is 32 years old on 23 July 2026 and does not turn 33 until 23 July 2027.

Indian forms usually ask for age in completed years on a stated date, so a person who is 32 years and 11 months old is still 32. Months and days matter when you are close to a limit.

Subtracting 1994 from 2026 gives 32 whatever the month, which is why that shortcut is only right for part of the year. The exact method subtracts from the largest unit to the smallest, borrowing when a result goes negative.

1. 1Subtract the birth year from the as-on year.
2. 2Subtract the birth month from the as-on month, and the birth day from the as-on day.
3. 3If the day difference is negative, add the number of days in the month before the as-on month and take one off the months.
4. 4If the month difference is now negative, add 12 to it and take one off the years.

Example: born 23 July 1994, age on 10 October 2026

You can verify this by walking forward. From 23 July 1994 to 23 July 2026 is 32 years. From 23 July to 23 September is 2 months. From 23 September to 10 October is 7 days to the end of September plus 10 days, which makes 17.

By subtraction: years 2026 − 1994 = 32, months 10 − 7 = 3, days 10 − 23 = −13. The days are negative, so borrow September's 30 days (−13 + 30 = 17) and take one off the months (3 − 1 = 2). This calculation works on dates alone, so the time of birth does not enter into it.

When months go negative too: a second borrowing example

The first example borrowed days only. Many ages also need a month borrowed from the year, which happens when the birth month is later in the calendar than the as-on month. Take someone born on 28 December 1999, as on 10 October 2026.

1. 1Years: 2026 − 1999 = 27.
2. 2Months: 10 − 12 = −2.
3. 3Days: 10 − 28 = −18.
4. 4Borrow the 30 days of September: days become −18 + 30 = 12, and months become −3.
5. 5Borrow a year: months become −3 + 12 = 9, and years become 27 − 1 = 26.

The result is 26 years, 9 months and 12 days, which is 9,783 days in total. Going forward to check: 28 December 1999 to 28 September 2026 is 26 years and 9 months, then 28 September to 10 October is 12 days.

Age in months, weeks or days

Some records, such as infant check-ups or service certificates, ask for age in a single unit. Convert from the exact result instead of dividing by an average.

• Total months = years × 12 + months. For 32 years and 2 months that is 386 completed months, plus 17 days.
• Total days = the actual day count between the two dates, not years × 365, because leap years add extra days. Here it is 11,767 days.
• Total weeks = total days ÷ 7. 11,767 days is exactly 1,681 weeks.

Check the day count by building it up. 32 years × 365 = 11,680 days. The leap days of 1996, 2000, 2004, 2008, 2012, 2016, 2020 and 2024 add 8 more, and the 79 days from 23 July to 10 October finish the count: 11,680 + 8 + 79 = 11,767.

Leaving the leap days out is the usual reason a hand-worked day count is a few days short.

Age as on a cut-off date

Forms for exams, jobs and schemes often ask for age as on a fixed date, not today. The same date of birth gives a different answer on each date, so always check the date in the notice.

Someone who is 31 on 1 July can be 32 by the closing date of an application. Eligibility rules are normally written in completed years on the stated date, so the years figure is what the form needs, while the months and days show how close you are to a limit.

Birthdays on 29 February

A person born on 29 February has a real birthday only in leap years. In other years, some systems treat 28 February as the birthday and others treat 1 March, so two tools can disagree by a day.

The table uses the borrowing method described above, which reaches 27 years on 1 March in a non-leap year. If an official form or document applies a different convention, follow that.

Mistakes when working out an age

• Subtracting the years only. A person born in December is still one year younger than that subtraction suggests until the birthday arrives.
• Treating every month as 30 days. The borrowed days must be the real length of the previous month: 28, 29, 30 or 31.
• Using today's date for a cut-off question. Check the as-on date printed on the form.
• Mixing day-first and month-first dates. 03/04/1998 is 3 April in India and 4 March in the US format.
• Adding one for the day of birth. Age counts elapsed time, so on the first birthday exactly one year has passed, not a year and a day.

The date difference guide covers the same subtraction for any two dates, and the days between dates guide shows how to get the plain day count if you need that instead.