Age Calculator
36 years, 3 months, 5 days
- 13,246
- Total days
- 1,892
- Total weeks
- Friday
- Born on a
- 268 days
- Next birthday in
The age calculator gives an exact age in years, months and days, plus the total days lived, the weekday you were born on and how long until the next birthday. It borrows from the real previous month rather than assuming 30 days, which is what makes the answer match how people actually state their age.
How it works
- Subtract the birth year from the target year to get a provisional year count.
- Subtract the months. If the result is negative, borrow twelve months and reduce the years by one.
- Subtract the days. If negative, borrow the real number of days in the month before the target date.
That last step is where most implementations go wrong. Borrowing a fixed 30 days gives a different answer depending on whether the month before was January or February, and the error is up to three days.
Total days is computed independently, by subtracting the two timestamps, so it is unaffected by the borrowing logic and can be used as a cross-check.
Examples
A straightforward age
Born
1990-06-15
On
2026-09-10
Result
36 years, 2 months, 26 days · 13,236 total days · born on a Friday
June 15 to September 10 is two full months plus 26 days, borrowing from August’s 31 days.
Borrowing from February
Born
2000-01-31
On
2026-03-01
Result
26 years, 1 month, 1 day
The day count borrows February’s 28 days rather than a fixed 30. Assuming 30 would report 26 years, 1 month and 3 days.
Frequently asked questions
Why do different age calculators disagree by a day or two?
Because they borrow different numbers of days when the day-of-month subtraction goes negative. Assuming 30 days is common and wrong; borrowing from the actual preceding month is correct and is what this tool does. The gap is largest around February.
How is the age of someone born on 29 February handled?
Their anniversary in a non-leap year is treated as 28 February, because the month arithmetic clamps to the last day that exists rather than rolling into March. That matches the convention used for most statutory purposes in England and Wales, but jurisdictions genuinely differ, some treat 1 March as the birthday, so treat it as this tool’s convention rather than a universal rule.
Is total days affected by leap years?
Yes, and correctly. It is calculated from the actual difference between the two dates, so every leap day in between is counted. It is the most reliable of the figures shown, and a good cross-check on the years-months-days breakdown.
Can I calculate an age at a past or future date?
Yes. The second field defaults to today but accepts any date on or after the birth date, which is how you work out how old someone will be at a future event.