Age Calculator

An age calculator states how much time has passed since a date of birth, counted the way people count birthdays: whole years first, then the months and days that have gone by since the last one.

That is not the same as dividing a number of days. A year is 365 or 366 days and a month is 28 to 31, so an age has to be read off the calendar rather than derived by arithmetic on a total.

• Enter the date of birth. The age appears as you enter it, measured to this moment from the clock on this device.
• Tick Include birth time to work to the minute. Left unticked, the day begins at midnight, so an age in hours is a lower bound.
• The next birthday is counted with the same rule as the age itself, so someone born on 29 February reaches it on 28 February in a year that has no leap day.
• The format buttons change how figures and dates are written. They do not change the result.
• Use Date to Date instead to measure between two dates you choose.

• Everything is calculated in your own time zone, from the clock on this device. Two people in different zones can legitimately see a different result for the same input.
• Daylight saving means some days are 23 or 25 hours long. The hour and minute counts follow the actual elapsed time, so they can differ from days multiplied by 24.
• Dates before 1582 are counted with today's calendar rules, which the Gregorian reform did not apply retroactively.