Age Calculator

About the Age Calculator

This works out an exact age between two dates — by default from a date of birth to today, but you can set the second date to any day to find an age in the past or future. Alongside the years-months-days figure it gives the same span expressed as total months, total weeks and total days, plus a countdown to the next birthday.

People reach for this to check eligibility cut-offs (school entry, pension, minimum-age rules), to fill in forms that ask for age at a specific date, to work out how old someone will be at a future event, or just out of curiosity about a milestone like the 10,000-day mark.

How it works — calendar maths, not division

The years/months/days figure is a true calendar difference, computed by borrowing the way you would by hand:

1. Subtract the years, months and days separately.
2. If the day-of-month goes negative, borrow a month and add the number of days in the preceding month (so borrowing across February adds 28 or 29 depending on the year).
3. If months then go negative, borrow a year (12 months).

The totals are derived independently:

• Total days = the raw difference between the two dates in days.
• Total weeks = total days ÷ 7, rounded down.
• Total months = years × 12 + months from the calendar breakdown.
• Next birthday = the birth month/day in the target year (or the following year if it's already passed), counted forward in whole days.

Assumptions and edge cases

• The "age at" date defaults to today and can be changed to any date; the date of birth must be on or before it, or the tool shows a validation message rather than a negative age.
• Dates are handled as whole calendar days — there's no time-of-day component, so two people born on the same date are the same age here regardless of the hour.
• Leap years are handled automatically by the calendar arithmetic; borrowing across February uses that year's real February length.
• 29 February birthdays: in a common (non-leap) year the "next birthday" rolls to 1 March, since 29 February doesn't exist that year. This matches how most systems treat leap-day birthdays.

Limitations

• Total months and total days describe the same span two different ways and won't reconcile by simple division — months vary from 28 to 31 days, so you can't multiply "total months" by 30 to get "total days." Both figures are correct; they just measure differently.
• It works in calendar dates only, with no time zones or hours, so it isn't suitable for precise duration timing (use a stopwatch or datetime tool for that).
• "Total weeks" is rounded down to whole weeks; leftover days aren't shown separately in that row.

Privacy

The dates you enter are used only for the calculation in your browser. No date of birth is transmitted, logged, or stored anywhere.