ToolPetal
Age calculator
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Client-side only. Gregorian calendar dates in your local time zone. Not legal advice on when someone reaches an age of majority, retirement or eligibility; the governing rule decides that.
Worked example: born 31 January, checked on 30 March
Take a birth date of 31 Jan 1995 and an as-of date of 30 Mar 2026. Years are easy: the 31st birthday was 31 Jan 2026. Months are where it gets awkward, because February has no 31st and 30 March is one day short of the next full month.
This page counts monthly anniversaries of the birth date. With the default rule, the one-month mark after 31 Jan 2026 is 28 Feb 2026 (the last day that exists). The two-month mark would be 31 Mar, which has not arrived. So the answer is 31 years, 1 month, and the days from 28 Feb to 30 Mar: 30 days. Total days lived: 11,381.
Here is why you can type the same two dates into four calculators and get four answers:
| Method | How the short month is handled | Result |
|---|---|---|
| Borrow previous month | 30 minus 31 plus 28 (February's length) | 31y 1m 27d |
| Borrow birth month | 30 minus 31 plus 31 (January's length) | 31y 1m 30d |
| Anniversary, last-day rule (this page, default) | 1-month mark is 28 Feb, count days from there | 31y 1m 30d |
| Anniversary, 1st-of-next-month rule | 1-month mark is 1 Mar, count days from there | 31y 1m 29d |
None of these is a bug. Years, total months (373) and total days match across all four. Only the leftover days move. If a form needs one specific number, ask which method the form uses. If it just needs days, use days between dates and skip the month question entirely.
Leap-day birthdays: the Feb 28 vs Mar 1 switch
Someone born on 29 Feb 2008 turns 18 in 2026, which is not a leap year. The rule you pick decides which day that happens:
| Question | Feb 28 rule | Mar 1 rule |
|---|---|---|
| 18th birthday falls on | Sat 28 Feb 2026 | Sun 1 Mar 2026 |
| Exact age on 28 Feb 2026 | 18y 0m 0d | 17y 11m 30d |
| Clears an 18+ check on 28 Feb? | Yes | No, one more day |
| 21st birthday (2029, common year) | Wed 28 Feb 2029 | Thu 1 Mar 2029 |
| Next real 29 Feb birthday | 2028 (turning 20) | 2028 (turning 20) |
The logic behind Feb 28: the person has finished the last day of February, so the year is done. The logic behind Mar 1: the 29th has not happened yet, so wait until the day after the 28th. Different statutes, insurers, and licensing offices land on different sides of this. The calculator does not know which one governs your case, so it lets you choose and labels the choice in the output.
What the totals actually count
- Total months is completed monthly anniversaries, the same count the years and months come from.
- Total weeks is total days divided by 7, with the remainder shown as days.
- Total days is calendar days from birth to the as-of date. The birth day itself is day zero, so someone born yesterday is 1 day old.
- Total hours is total days times 24. No birth time, no daylight saving, no time zone travel.
- Next birthday shows 0 days and "today" when the as-of date is the birthday.
Limitations
- Gregorian calendar only, extended backwards for old dates. Dates before a country switched from the Julian calendar (1582 in parts of Europe, 1752 in Britain and its colonies) will not match records written at the time.
- No East Asian age reckoning, where a newborn counts as one. South Korea moved official ages to the international system in 2023; this page uses that system only.
- No time of birth. A baby born at 11:58 pm and one born at 12:02 am the next day get different dates here, because that is what their birth certificates say.
- No eligibility decisions. Pension, school entry and drinking-age rules often use a cutoff date or "attains age on the day before" wording that a plain age figure does not capture.
FAQ
How does this handle a 29 February birthday?
You pick the rule. In common years the birthday either falls on 28 February (the default) or on 1 March. The choice changes the exact age on those two days and the date of the next birthday. Neither is universally correct; legal systems and institutions differ, so use the one your situation follows.
Why does a 31 January birth date give odd month counts?
Because most months have no 31st. The calculator counts each month as an anniversary of the birth date. When that day does not exist, the same rule as the leap-day setting applies: the last day of the short month, or the 1st of the next month. Anniversaries are always measured from the original birth date, so a 31 January birthday does not drift to the 28th for the rest of the year.
Can I find someone's age on a past or future date?
Yes. Change the Age as of date to any day. Leave it blank for today. If the as-of date is before the birth date, the page tells you how many days until the birth instead of showing a negative age.
Why do other age calculators show a different number of days?
When the day of the month in the as-of date is smaller than the birth day, a calculator has to borrow days from some month, and tools disagree on which one. Some borrow the length of the previous month, some the birth month, and some count from the last monthly anniversary as this page does. Years and total days always agree; the leftover days can differ by one to three.
Is the total hours figure exact?
No. It is total calendar days multiplied by 24. It ignores the time of birth, the time zone you were born in, and daylight saving shifts. Treat it as a fun number, not a measurement.
Is my date of birth uploaded?
No. Dates are read and calculated in this browser tab. Nothing is sent to ToolPetal or stored after you close the page.