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Date of Birth Calculator

Find a date of birth from an age. With the age in years only, you get the range of possible dates. With months and days as well, you get the exact date.

Two kinds of answer

  • Years only. One age in years fits a whole year of birth dates. Someone who is 25 on 1 November 2026 was born between 2 November 2000 and 1 November 2001. The calculator shows the first and last possible date, and the birth year or the two possible birth years.
  • Years, months and days. If you enter months and days as well, even if they are zero, the calculator gives one exact date of birth, with the day of the week.

How to use it

  1. Enter the age in years. Leave Months and Days empty if you do not know them.
  2. Set Age at the date of. It is today by default. Use another date if the age was given on an earlier or later day, for example on a form or a document.
  3. Read the range or the exact date.

How the date is worked out

The calculator takes the extra days off the date first, and then takes off the years and months. For 25 years, 2 months and 5 days on 20 March 2025, it removes 5 days to reach 15 March 2025, and then 302 months, which gives 15 January 2000. If a day does not exist in the earlier month, the last day of that month is used.

Limits

The result is a calculation from the age that you enter. It cannot tell you a real person's date of birth, and it is not a substitute for a birth certificate or an official record.

Related calculators

Check the result with the age calculator. See also age in years, age difference, and date difference.

Frequently asked questions

How do I find a date of birth from an age?

Enter the age and the date on which it applies. With years only you get the range of possible dates, and with months and days you get the exact date.

If someone is 25, when were they born?

In the year range ending 25 years before today, and starting 26 years before today plus one day. The calculator shows the dates.

Can I use a date other than today?

Yes. Change Age at the date of to the day on which the age was given.

Is the result exact?

Only if you enter the months and days. With years only, it is a range.