Understanding the result
The main result is age as completed years, months and days. Below it you will see the same age as total months, total weeks and total days, which are useful for milestones such as "10,000 days old".
If "Show next birthday" is on, you also see the date of the next birthday, how many days remain until it and the age being reached.
What is an age calculator?
An age calculator measures the time from a date of birth to a reference date, usually today. Age is normally quoted in completed years, but months and days are handy for babies, for eligibility rules and for anniversaries.
You can also calculate age on a past or future date, for example to check how old someone was at an event or how old they will be on a particular day.
How it works
Age is a calendar difference. Whole months are counted forward from the date of birth; every 12 months is a completed year. The days left over after the last whole month are the "days" part.
A person turns a year older on the birthday itself, so the day before the birthday the age is still one year younger and the "days" part is the count of days since the last monthly anniversary.
Total days is the exact number of days between the two dates. Total weeks is that number divided by 7, rounded down.
Examples
Born 17 April 1992, on 20 September 2026
Age is 34 years, 5 months and 3 days, which is 12,574 days or 1,796 full weeks. The next birthday is 17 April 2027, when the age reached is 35.
Born on 29 February 2000
In years without a 29 February, this calculator treats the birthday as 28 February, the same rule it uses for month arithmetic. On 28 February 2001 the age is 1 year exactly; on 1 March 2001 it is 1 year and 1 day.
Age on a future date
Set "Calculate age on" to a custom date, such as a planned retirement or exam date, to see exactly how old a person will be on that day.
Things to keep in mind
- Leaplings (people born on 29 February) are treated as having their birthday on 28 February in common years. Some legal systems use 1 March instead. If the rule matters, for example for a legal age, check the rule that applies.
- The calculator uses the date of birth and the reference date as calendar dates. It does not consider the time of birth or time zones, which can matter for births near midnight across time zones.
- Some cultures count age differently, for example counting a newborn as one year old. This tool uses the common Western convention of completed years.
- Your date of birth is not stored, is not added to the address in your browser and is never sent to analytics. Closing or reloading the page clears it.