What does the age calculator do?
Working out an exact age sounds simple until months of different lengths and leap years get involved. This calculator counts the complete calendar years and months between a date of birth and a second date (today by default), then the remaining days. It is the same method used on official forms, school admissions and insurance applications that ask for your age “in years and months”.
It also shows your age as a total number of months, weeks and days, the day of the week you were born, and how long it is until your next birthday. Change the “age on” date to find how old someone was, or will be, on any date in the past or future.
How to use it
- Choose the date of birth with the date picker or type it.
- Leave Age on as today, or pick another date, such as an exam cut-off date or a future event.
- Read the age in years, months and days, plus the totals and your next birthday.
How age is calculated
The calculator finds the largest number of whole months you can add to the date of birth without passing the target date, then counts the leftover days. Whole months are split into years and months. When a month is shorter than your birth day (for example, someone born on the 31st), the date is clamped to the last day of that month, which is how most legal and administrative systems treat it.
People born on 29 February celebrate on 28 February in common years in this calculator. Some countries legally use 1 March instead, so check local rules if a legal deadline depends on it.
Example
Someone born on 15 May 1990 is 36 years, 5 months and 9 days old on 24 October 2026. That is 13,311 days, or 1,901 weeks. They were born on a Tuesday, and their 37th birthday on 15 May 2027 is 203 days away.
More worked examples
Leap-year birthday: someone born on 29 Feb 2000 is exactly 26 years old on 28 Feb 2026 in this calculator, which treats 28 February as the birthday in common years.
Common mistakes to avoid
- Subtracting years only. Someone born in December 2000 is 25, not 26, in October 2026.
- Typing dates in the wrong order. 04/05 means 4 May in many countries and April 5 in the US; the date picker avoids this.
- Counting the end date as a full day. Age counts complete days. To include the end date, use the date difference calculator.
Sources and methodology
The calculations on this page follow these published standards and references. The code is covered by automated tests against known values.
- Gregorian calendar leap-year rule (years divisible by 4, except centuries not divisible by 400)
- ISO 8601 – Date and time format