By the Tooliday Team. Last updated 14 November 2026.
Most of us know our age in years. But forms for exams, pensions, school admissions and visas often ask for age on a particular date, sometimes in years, months and days. Working it out by hand is easy once you know the order of steps. You can always check the result with our Age Calculator.
The method: subtract, then borrow
Write the later date (today, or the date you are checking) above the date of birth and subtract in three columns: days, months, years. If a column goes negative, borrow from the next column, just like ordinary subtraction.
Worked example
Date of birth: 15 August 1995. Date to check: 14 November 2026.
- Days: 14 − 15 is negative, so borrow one month. The month before November is October, which has 31 days, so the days become 14 + 31 − 15 = 30, and the month count drops by one.
- Months: November is month 11 and August is month 8, so 11 − 8 = 3. After borrowing one, that is 2 months.
- Years: 2026 − 1995 = 31.
The answer is 31 years, 2 months and 30 days. A quick check: 15 August 1995 plus 31 years is 15 August 2026, plus 2 months is 15 October 2026, and 30 more days reaches 14 November 2026.
Which month length do you borrow?
This is where people get different answers. The usual convention is to borrow the number of days in the month just before the later date. Some official forms use a fixed 30 days instead. If a form gives you its own rule, follow it. When no rule is given, the calendar method above is the most common.
Total days lived
From 15 August 1995 to 14 November 2026 is 11,414 days. If you simply divide by 365 you get 31.27 years, which suggests 31 years and about 3 months. The calendar answer is 31 years and 2 months. The difference comes from leap years: there were eight leap days in this period, so each calendar year is on average slightly longer than 365 days. Dividing by 365.25 gives 31.25 years, which is much closer.
How leap years work
A year is a leap year if it is divisible by 4, except century years, which must be divisible by 400. So 2024 was a leap year, 1900 was not, and 2000 was. A person born on 29 February has an official birthday only every four years. In non-leap years, the legal birthday is generally treated as 28 February or 1 March depending on the country and the purpose, so check the rule that applies to you.
Common mistakes
- Subtracting only the years and forgetting that the birthday has not yet come this year.
- Using the wrong order of dates, which gives a negative answer.
- Borrowing 30 days every time when the month actually has 28, 29 or 31.
- Mixing date formats. Write 03/04/2026 as day/month or month/day consistently.
Try it yourself
Enter any date of birth and a comparison date in the Age Calculator to get years, months, days and total days at once. It runs in your browser, so your dates are not sent to our servers.