How it works
The calculator compares year, month and day components, borrowing a month when the day difference is negative. Total days counts the absolute difference, and the next birthday is the next occurrence of the birth month and day after today.
- Uses the local calendar; leap days are handled by the date arithmetic.
Why it matters
Age appears in forms, eligibility checks and anniversaries, and the off-by-one errors are almost always leap days or a birthday that has not happened yet this year. A calendar-based calculation avoids the drifting error of dividing days.
A worked example
Born on 10 May 1990, on 30 October 2026 the exact age is 36 years, 5 months and 20 days — 13,322 total days, with the next birthday 192 days away.
Common mistakes
- Dividing total days by 365.25 and rounding.
- Ignoring leap days in long ranges.
- Using a time zone that shifts the birth date by a day.
Practical tips
Use the local calendar date for forms; use UTC only for machine comparisons. If you need an age in months for a child, count completed months rather than converting from days.
How to use it
- Open the tool. Everything runs in your browser tab.
- Paste or type your input, then choose the action you need.
- Check the result and copy it with one click.
Common questions
How is the age calculated?
Calendar arithmetic from the selected date: whole years, then months, then days, plus total days and the next birthday.
How are leap days handled?
The date arithmetic uses the real calendar, so 29 February is handled without special input.
What happens with a future date?
The tool refuses it, because an age cannot be negative.
Is this tool really free?
Yes. There is no account, no paywall and no usage limit. Tools App is funded by aumenso, the studio behind it.
Is anything I enter uploaded?
No. The tool runs in your browser tab; what you enter is never sent to us and never stored.