Age Calculator
The calculator works out an age from a date of birth on any reference date: full years, the remaining months and days, and the total number of days, weeks and hours lived.
It also shows which weekday you were born on and how many days remain until the next birthday.
Age
36 years 2 mo 25 days
Born on a: Tuesday
Total days
13,235
Total weeks
1,890
Total full months
434
Total hours
317,640
Until the next birthday
279 days — May 15, 2027, turns 37
Age is counted by the calendar: full years first, then the remaining months and days. Leap years are handled automatically.
How age is counted
Age is counted by the calendar rather than by dividing days by 365. Full years come first: if the day and month have not arrived yet this year, the year does not count. The remaining months and days are added after that.
Example: someone born on 15 May 1990, measured on 9 August 2026. That is 36 full years, then two months from 15 May to 15 July, then 25 more days to 9 August — 36 years, 2 months and 25 days.
Why dividing days by 365 fails
- Every fourth year has 366 days, so about nine extra days accumulate over 36 years.
- The mean year is 365.2425 days, not 365, so the division always understates the age.
- Months are unequal: 15 January to 15 February is 31 days, 15 February to 15 March is 28 or 29.
- Calendar counting matches how age is recorded on documents; division does not.
Age in different units
| Full years | Days (approx.) | Weeks (approx.) | Months (approx.) |
|---|---|---|---|
| 1 | 365 | 52 | 12 |
| 5 | 1,826 | 261 | 60 |
| 10 | 3,653 | 522 | 120 |
| 18 | 6,575 | 939 | 216 |
| 30 | 10,958 | 1,565 | 360 |
| 50 | 18,263 | 2,609 | 600 |
Birthdays on 29 February
For someone born on 29 February, the birthday falls on 28 February in common years — the calendar simply has no such date. The calculator follows the same rule and clamps to the last day of the month.
Legal deadlines treat that shift differently from country to country, so for paperwork follow local rules rather than this calculation.
Frequently asked questions
How do I calculate age from a date of birth?
Subtract the birth year from the current year and take one off if the birthday has not happened yet this year. The calculator does that automatically and adds the remaining months and days.
How many days have I lived?
The calculator shows the exact number of days between the date of birth and the reference date, including every leap day in between.
What weekday was I born on?
It is shown under the age. The weekday is recomputed from the calendar, so it is correct for any date in the 20th and 21st centuries.
Why isn't the age in months just years times twelve?
It is: the calculator reports full months as years × 12 plus the leftover months. Differences only appear against rough estimates that assume 30-day months.
Can I calculate an age on a future date?
Yes — put any day in the reference date field and the calculator shows the age reached by then.
Updated: 2026-08-09