Age on a date
Your age on a given date is the number of birthdays you have completed by then. Enter a date of birth and an as-of date, and this calculator shows the age in years, months and days, the total number of days, and how long until the next birthday. The as-of date does not have to be today. A button fills in today's date in your own calendar, and the dates stay in the page: they are not saved, sent or added to the address.
Calendar years, months and days
The years, months and days follow one rule, stated so you can check it. Add whole months to the birth date until the next addition would pass the as-of date. That point is the anchor. Years are the whole months divided by twelve, the months are the remainder, and the days are counted from the anchor to the as-of date. Someone born on 6 November 2000 is exactly 26 years, 0 months and 0 days old on 6 November 2026, which is 9,496 days in total. The day before, they are 25 years, 11 months and 30 days old and have completed 25 birthdays.
The birth day itself is not counted in the total. From 28 February 2024 to 1 March 2024 is 2 days, because 2024 is a leap year and contains 29 February. Day counts use calendar dates rather than clock hours, so changes to daylight saving time never add or remove a day.
Leap-day and end-of-month rules
Months have different lengths, so any age calculator has to make a choice when the birth day does not exist in the target month. This one adds months to the original birth date and clamps the day to the last day of a shorter month. A birth date of 31 January plus one month is 28 February in a common year, so someone born on 31 January 2001 is 1 month and 0 days old on 28 February 2001. A person born on 28 February 2022 is 1 month and 3 days old on 31 March 2022, because 28 March is the anchor and three days remain. Other tools may report one month there, which is also reasonable; the steps under the result show which convention was used.
People born on 29 February meet a second question: when is the birthday in a common year? You can choose 28 February or 1 March. The choice changes the completed-birthday count only on the days between those dates. For someone born on 29 February 2000, on 28 February 2025 the count is 25 if birthdays fall on 28 February and 24 if they fall on 1 March. The years, months and days stay at 25 years, 0 months and 0 days either way, since they come from the anchored months. This is a planning convention, not legal advice, and laws and organisations may set their own rule for official purposes.
Next birthday
The next birthday is this year's anniversary if it has not yet passed, and next year's otherwise. If today is the birthday, the countdown is zero days and the page says so. The countdown counts calendar days between the as-of date and that anniversary, and it also shows the age being reached. For a leap-day birthday, the anniversary in a common year follows the rule you picked above. A birthday after 2100 is reported as out of range.
Days versus elapsed hours
The table of totals multiplies days by 24, 1,440 and 86,400 to give hours, minutes and seconds. Those are labelled calendar-day equivalents, and they are not a measure of elapsed time. A real count would need your time of birth and the time zone, plus the daylight-saving changes in between. Without those, a precise-looking number of seconds would be false precision. For the clock time between two moments on the same day, use the hours between times calculator; calendar age and clock duration answer different questions.
Worked examples and questions
| Born / as of | Result |
|---|---|
| 6 Nov 2000 / 6 Nov 2026 | 26 y 0 m 0 d, 9,496 days |
| 6 Nov 2000 / 5 Nov 2026 | 25 y 11 m 30 d, birthday in 1 day |
| 28 Feb 2024 / 1 Mar 2024 | 2 days |
| 31 Jan 2001 / 28 Feb 2001 | 1 month, 0 days |
| 28 Feb 2022 / 31 Mar 2022 | 1 month, 3 days |
For the number of days between any two dates, or to add months to a date, use the date calculator; this page is built around a birth date and a birthday. If you track working hours, the time card calculator handles clock times and pay, and it does not calculate age.
How do I calculate age on a specific date?
Count completed birthdays up to that date. For years, months and days, add whole months to the birth date until you reach the last date that is not after the target, then count the remaining days.
Why do different age calculators give different months and days?
Months vary in length, so tools differ on how to handle birth days like the 31st and on 29 February. This one names its rule in the steps. The difference is usually a few days in the day count, and the completed years differ only for people born on 29 February.
How are leap-day birthdays counted?
You choose 28 February or 1 March for common years. The completed-birthday count follows your choice, while the anchored months keep a person born on 29 February at the same years, months and days either way.
How many days until my next birthday?
The calculator counts calendar days from the as-of date to the next anniversary, and shows zero when the as-of date is the birthday itself.
Are the seconds exact?
No. They are days multiplied by 86,400, because the calculator has no time of birth or time zone.
Privacy and scope
The calculator works on dates only. It does not give medical, biological or legal age, does not decide eligibility for school, insurance or benefits, and does not apply the age customs of other calendars or cultures. The supported range is 1 January 1900 to 31 December 2100, and the birth date must not be after the as-of date.