Birth Year Calculator

Find your possible birth years from a completed age and reference date, or use birthday information to narrow the answer.

Your inputs

Calculated in your browser. Your inputs stay on this device.

Starting values are examples. First click or keyboard focus clears an example so you can enter yours. Reset restores the examples.

Your result

Enter your values to calculate.

Compare scenarios

Keep up to three results and their inputs during this visit. Reset clears the comparison.

Behind the answer

If the birthday has occurred: reference year − age. Otherwise subtract one more year. Unknown birthdays define an inclusive date-of-birth interval.

How to use this calculator

Choose a reference date and enter completed years. If the birthday is unknown, both possible years are shown. Add birthday information to narrow the result. Reverse mode reuses the calendar-age engine; February 29 anniversaries use February 28 in non-leap years.

Enter calculate, age in completed years, reference date and review the remaining options.
Select Calculate or change a value to update the result. Read the result label and units before copying.
Use Reset to restore the worked starting values.

Formula and method

If the birthday has occurred: reference year − age. Otherwise subtract one more year. Unknown birthdays define an inclusive date-of-birth interval.

Calendar age uses the Gregorian calendar and a February 28 anniversary convention for leap-day births. Legal age rules can differ. A completed age alone usually cannot identify one birth year.

Worked example

Someone aged 16 on 12 November 2026 was born between 13 November 2009 and 12 November 2010, inclusive. If their birthday has occurred in 2026, their birth year is 2010.

Questions about birth year calculator

What year was I born if I am 16?

On 12 November 2026, age 16 allows birth years 2009 or 2010. Your birthday determines which one: 2010 if it has occurred, otherwise 2009. Select a different reference date to answer the same question for another year.

What assumptions should I check?

Calendar age uses the Gregorian calendar and a February 28 anniversary convention for leap-day births. Legal age rules can differ. A completed age alone usually cannot identify one birth year.

Are my inputs saved?

Calculations run in your browser. We store only tool IDs for favorites and recent tools. A calculation link contains your inputs only when you explicitly choose to copy one.