Your age in whole years is easy. Your exact age in years, months, and days takes a little more care, because months have different lengths and leap years add an extra day. The borrow method below handles all of that without any special tables.
How it works
Start with the current date and your birth date. Subtract days first, then months, then years, borrowing when a number goes negative. When days go negative, borrow one month and add the number of days in the previous month. When months go negative, borrow one year and add 12 months. The result is your exact age, and it automatically accounts for leap years because you work with real calendar months.
Step by step
- Write the current date as day, month, year, and your birth date the same way.
- Subtract the birth day from the current day. If the result is negative, borrow one month and add the days in the previous month.
- Subtract the birth month from the current month, after any borrowing. If negative, borrow one year and add 12.
- Subtract the birth year from the current year, after any borrowing.
- Read the three numbers as years, months, and days.
- Double-check by adding your age back to your birth date; you should land on today.
Worked example
Born 14 March 1990, today 25 October 2026. Days: 25 – 14 = 11. Months: 10 – 3 = 7. Years: 2026 – 1990 = 36. Exact age: 36 years, 7 months, 11 days. A trickier case: born 28 January 2000, today 10 February 2026. Days: 10 – 28 = -18, so borrow one month (January has 31 days): -18 + 31 = 13 days, and months drop by one. Months: 2 – 1 (borrowed) – 1 = 0. Years: 2026 – 2000 = 26. Exact age: 26 years, 0 months, 13 days.
Common mistakes
- Subtracting years first and then trying to fix months and days afterwards, which scrambles the borrowing.
- Borrowing 30 days for every month instead of the actual days in the previous month.
- Forgetting that February has 29 days in a leap year when borrowing across it.
- Counting the birth day itself as a full day lived, which adds one day too many.
Try it with the free tool
You can follow every step above by hand, but the free tool below does the same calculation instantly. Try your own numbers in it, then check one result by hand so you trust the method as well as the answer. Open the full tool here: open the tool.
Checklist before you finish
- Write down every input number first, with its unit, before you calculate anything.
- Work through the steps in order, and do not skip the unit conversions.
- Check the answer against the worked example above: is it the right size, and does the direction make sense?
- Round only at the end, and keep the unrounded figure for any follow-up calculation.
Practice with your own numbers
Pick three cases of your own and work each one by hand. First, try a simple round-number case you can check mentally. Second, try a realistic case with awkward numbers, the kind you will actually meet. Third, try an edge case, such as a very small or very large input, and confirm the answer still behaves sensibly. If any case gives a surprising result, re-check the units and the formula step by step before you trust it.
If your answer looks wrong
Most errors come from a small set of causes. Check that you used the same units throughout, that you divided where the formula divides and multiplied where it multiplies, and that you applied any percentage as a decimal. Check the order of operations: powers and brackets come before multiplication and division, which come before addition and subtraction. Finally, test the method on the worked example in this guide. If your method reproduces the example answer, the method is right and the inputs deserve a second look.
Quick tips
If you only need whole years, compare month and day: if your birthday has not happened yet this year, subtract one from the year difference. For official forms, use the date on your birth record, not the date you celebrate.