This age calculator finds the completed years, months, and days between a date of birth and another calendar date. It compares the year, month, and day numbers and borrows a month or a year when the day or month difference would otherwise be negative. The result is a calendar age, not a count of hours.
Leave "Age on date" blank to use today's date in your own time zone. The sample birth date in the form is 1 January 1990, but the worked examples below use fixed dates so the explanation does not change tomorrow. If the second date is earlier than the birth date, the year count can come out negative. Put the later date in the age-on field.
How to use this calculator
- Enter the date of birth.
- Enter the date you want the age on, or leave it blank for today.
- Press Calculate. The headline is the completed years. Months and days appear underneath.
- Read both lines together. "36 years" plus "9 months and 7 days" is the full result, not 36 years alone.
How completed years, months, and days are borrowed
The calculator subtracts the birth year, month, and day from the target year, month, and day. Months are numbered with January as 1 in this explanation. If the day difference is negative, it borrows the length of the month before the target month and reduces the month difference by one. If the day difference is still negative, it borrows one more month, using the length of the month before that. A birth date on the 31st and a target date of March 1 needs that second borrow, because February is shorter than the day gap. If the month difference is then negative, it borrows one year and adds 12 months.
Leap days are handled only through those month lengths. February has 29 days in a leap year and 28 otherwise. Someone born on 29 February is not given a special legal rule. Under this borrowing method, 1 March is an exact number of years later when the target year is not a leap year.
The headline and the detail line use singular wording when the count is 1: "1 year", "1 month", and "1 day". Other counts use the plural, including zero.
Formula
years = target year − birth year months = target month − birth month days = target day − birth day If days < 0, add the length of the previous month and subtract 1 month. If days are still < 0, add the length of the month before that and subtract another month. If months < 0, add 12 months and subtract 1 year.
The length of a month is the real calendar length, including leap-day February. The calculator does not convert the span into an average 30.437-day month, and it does not divide total days by 365.25.
A blank target date means the current local calendar date when you press Calculate. Two people in different time zones can still be on different calendar dates near midnight, so "today" is the date on the device running the page.
Worked age examples
Born 15 January 1990, age on 22 October 2026
Year difference 2026 − 1990 = 36. Month difference October − January = 9. Day difference 22 − 15 = 7. Nothing is negative, so nothing is borrowed. The calculator shows 36 years, then "9 months and 7 days beyond the last birthday."
The last birthday on or before 22 October 2026 is 15 January 2026. Nine months after 15 January is 15 October, and seven days after that is 22 October. The borrowed-calendar result matches that count on this ordinary date.
A one-day-old infant, and an age of zero
Born 31 December 2010, age on 1 January 2011. The calculator shows 0 years, then "0 months and 1 day beyond the last birthday." The day is singular because the count is exactly one.
Born 15 June 1995, age on 15 June 1995. The calculator shows 0 years, then "0 months and 0 days beyond the last birthday." The same calendar date is an age of zero, not one day. This tool does not add a day to include the birthday as a completed day of life.
29 February, and a birth date on the 31st
Born 29 February 2000, age on 29 February 2024. Both dates are leap days. The calculator shows 24 years, then "0 months and 0 days beyond the last birthday." Age on 1 March 2025, a non-leap year, shows 25 years and "0 months and 0 days beyond the last birthday." The borrow uses February 2025's 28 days to fill the gap from the 29th to 1 March, so this tool treats 1 March as the anniversary. Age on 28 February 2026 shows 25 years and "11 months and 30 days beyond the last birthday." February 28 has not yet reached that 1 March anniversary.
Born 31 August 1988, age on 1 March 2024. The day gap is 1 − 31 = −30. February 2024 has 29 days, so the first borrow leaves −1 day and then a second borrow adds January's 31 days. The calculator shows 35 years, then "5 months and 30 days beyond the last birthday." On the next day, 2 March 2024, February's 29 days exactly cover the gap from the 31st, and the result is 35 years and "6 months and 0 days beyond the last birthday." The extra month appears because the short February no longer needs the second borrow.
Ages this calculator shows for fixed dates
| Date of birth | Age on | Headline | Detail line |
|---|---|---|---|
| 15 Jan 1990 | 22 Oct 2026 | 36 years | 9 months and 7 days beyond the last birthday. |
| 31 Dec 2010 | 1 Jan 2011 | 0 years | 0 months and 1 day beyond the last birthday. |
| 15 Jun 1995 | 15 Jun 1995 | 0 years | 0 months and 0 days beyond the last birthday. |
| 29 Feb 2000 | 29 Feb 2024 | 24 years | 0 months and 0 days beyond the last birthday. |
| 29 Feb 2000 | 1 Mar 2025 | 25 years | 0 months and 0 days beyond the last birthday. |
| 29 Feb 2000 | 28 Feb 2026 | 25 years | 11 months and 30 days beyond the last birthday. |
| 31 Aug 1988 | 1 Mar 2024 | 35 years | 5 months and 30 days beyond the last birthday. |
What this calendar age does not count
The result is not a count of days lived, and it is not an exact number of hours. Time of birth is ignored because the fields are dates. Someone born late on 15 January and someone born just after midnight have the same result on this page.
Legal ages for driving, contracts, or benefits sometimes use a specific rule for a 29 February birthday, or they count the birthday as the moment a year is completed at a particular hour. This calculator's March 1 convention in non-leap years is a consequence of the borrow method, not a statement of the law where you live.
The second borrow around February means a birth date on the 31st can show a sudden month change between March 1 and March 2 in a leap year. That jump is described in the example above so it is not a surprise. Other target dates use a single borrow and do not show a negative day count.
Frequently asked questions
What happens if I leave the age-on date blank?
The calculator uses today's date on the device where the page is open, in that device's local time zone. The field is optional. Fill it when you want a fixed date instead of today.
How does this calculator treat a February 29 birthday?
It uses month lengths, not a separate leap-day rule. Born on 29 February 2000, the age on 29 February 2024 is exactly 24 years. The age on 1 March 2025 is exactly 25 years. The age on 28 February 2026 is 25 years, 11 months, and 30 days, so February 28 is still before that anniversary in this tool.
Why can the month count jump at the start of March?
A birth date on the 31st can need two month-borrows when the target is March 1, because February is shorter than the day gap. Born 31 August 1988, the age on 1 March 2024 is 35 years, 5 months, and 30 days. On 2 March 2024 it is 35 years and 6 months. The second date no longer needs the extra borrow.
What if the age-on date is before the date of birth?
The same subtraction runs anyway, and the year can be negative. That is not a useful age. Enter the birth date first and a target on or after that date.
Does the result count the birthday as a full day lived?
No. On the date of birth the calculator shows 0 years and 0 months and 0 days. The next calendar day is 1 day. It is a difference between dates, not an inclusive count of days alive.
Related ClearCalc pages
- Days between two dates The elapsed day count, including weekends. It does not borrow months the way this age result does.