Date of Birth Calculator

Know someone's age but not their birthday? Enter the age to find the year they were born and every date of birth that fits.

Calculated on your device. Nothing you enter is sent or saved.

Born in

2001or 2000

2001 if the birthday has already passed this year, 2000 if not.

8 Oct 2000earliest date of birth
7 Oct 2001latest date of birth

Add months and days to the age to get one exact date.

Calculators people use alongside the Date of Birth Calculator.

Birth year from age

How the date of birth calculator works

By Reviewed How we check facts

In short

Subtract the age from the current year. If the birthday has already happened this year, that is the birth year; if not, take one more year off. Someone who is 25 on 7 October 2026 was born between 8 October 2000 and 7 October 2001.

Possible birth years for one age
2
Possible birth dates
365 or 366
With age in years, months and days
1 exact date

How to find a date of birth from an age

  1. Enter the age in years. Add months and days too if you know them, for example from a medical or school form.
  2. Leave On date as today, or set the day that age was true (the date on a document, for example).
  3. Read the birth year and the earliest and latest possible dates of birth. With months and days filled in, you get one exact date.

What year was I born if I am a certain age?

An age in whole years covers a full year of possible birthdays, so it always points to two calendar years. The deciding question is whether the birthday has passed yet this year.

Birth year for common ages, measured in 2026
AgeBirthday already this yearBirthday still to come
162,0102,009
182,0082,007
212,0052,004
252,0012,000
301,9961,995
401,9861,985
501,9761,975
651,9611,960

Finding an exact date of birth from years, months and days

Ages written as years, months and days (common on baby and medical records) identify a single date. The calculator steps back the days first, then the months and years, which is the exact reverse of how the Age Calculator counts forward.

Month ends

Stepping back from a 31st into a shorter month lands on that month's last day, the same rule the age calculator uses going forward, so the two tools always agree.

When people use a birth year calculator

  • Filling in a form that asks for a year of birth when you only know someone's age.
  • Family history: turning an age on a census or record into a likely birth year.
  • Checking which generation someone belongs to with What Generation Am I?.

Common questions

How do I calculate my birth year from my age?

Take the current year and subtract your age. If you have not had your birthday yet this year, subtract one more.

If I am 18, what year was I born?

Measured in 2026, you were born in 2008 if you have already had your birthday this year, or in 2007 if not.

Why does the calculator show a range of dates?

An age in whole years is true for a whole year of birthdays. Add the months and days of the age to narrow it to one exact date.

Can I find an age-based birth year for a date in the past?

Yes. Set the On date to the day the age was recorded, such as the date on a census, and the calculator works from that day.

Sources

  1. Gregorian calendar · Encyclopaedia Britannica
  2. What is a leap year? · Royal Museums Greenwich