Age Calculator
Enter a date of birth and the date to measure on — today, or any other date. The calculator gives the age in completed years, months and days, the total number of days, and how many days remain until the next birthday.
Answer
Answer
An input above needs attention before this can be calculated.
How it works
Age in years is the number of birthdays that have passed. Someone born on 15 May 1990 is 36 from 15 May 2026 until the day before 15 May 2027. Months and days then count forward from the most recent birthday, so on 19 October 2026 the same person is 36 years, 5 months and 4 days old.
Measuring on a date other than today is useful for forms that ask for age on a set date, school entry cut-offs or the age someone will be at an event. The calculator uses the date you enter and nothing from your device except today’s date as a starting value.
People born on 29 February have a birthday that exists only in leap years. In other years the calculator counts it on 28 February, which is the convention used for this site’s age arithmetic; some legal systems use 1 March instead, and that difference is stated wherever it matters.
Formula
age = birthdays passed by the date, then months and days since the last birthday
Years are the birthdays that have occurred on or before the measuring date. Months and days are counted forward from the last birthday along the calendar.
Worked examples
- Try these numbers
Born 15 May 1990, measured on 19 October 2026
- The 36th birthday was 15 May 2026, so the age is 36 years.
- From 15 May to 15 October is 5 months; 15 to 19 October is 4 days.
- The next birthday, 15 May 2027, is 208 days away.
36 years, 5 months and 4 days — 13,306 days lived.
- Try these numbers
On the birthday itself
- 10 March 2026 is the 26th birthday.
- No months or days have passed since it.
Exactly 26 years old, with 0 days to the birthday.
- Try these numbers
Leap-day birthday in an ordinary year
- 2026 has no 29 February.
- The birthday is counted on 28 February, so this is the 22nd birthday.
Exactly 22 years old on 28 February 2026.
Inputs and results
- Date of birth
- The day the person was born.
- Age on
- The date to measure age on. Starts as today.
- Age
- Completed years, then months and days since the last birthday.
- Days alive
- Calendar days from the date of birth to the measuring date.
- Days to next birthday
- Days from the measuring date to the next birthday, or 0 on the birthday itself.
When to use it
- Filling in a form that asks for age on a particular date.
- Checking how old a child will be on a school or sports cut-off date.
- Counting the days until a birthday, or how many days someone has lived.
Common mistakes
- Measuring on the wrong date: the second field defaults to today, so change it when a form asks for age on another date.
- Expecting months to be a fixed 30 days; calendar months vary, and the breakdown follows the real calendar.
- Typing the date in day-month order into a field that expects the calendar picker’s format; use the date picker to avoid it.
What it does not do
- It does not use the time of birth, so it cannot say whether someone has reached an age on the day of birth itself in another time zone.
- It does not determine legal age for any purpose; rules on when a person attains an age differ between countries.
- It uses the Gregorian calendar for all dates, including historic ones.
Method and assumptions
The age in years is the largest whole number of years that can be added to the birth date without passing the measuring date. Months are then added the same way, and the remaining days are counted.
Total days is the difference between the two dates on one continuous day count, including leap days. The next birthday is the birth date in the following year, moved to 28 February when it would fall on a missing 29 February.
Assumptions
- A 29 February birthday falls on 28 February in non-leap years.
- Age is measured in whole days, without the time of birth.
Edge cases
- A measuring date before the date of birth is refused with a message on that field.
- On the birthday, the days to the next birthday are 0.
- Someone born on 31 January has a month mark on the last day of shorter months.
Sources and corrections
This calculator uses an elementary formula, so it needs no outside data source. The method, the rounding rules and how a reported error is corrected are set out in the site standards.
Result looks wrong?
Send the inputs you used and the answer you expected. Every report is checked against the formula and its tests, and confirmed errors are corrected in public.