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Birth From Death Date Calculator

Created by Davide Borchia
Reviewed by Komal Rafay
Last updated: Jan 18, 2024


Our birth from death date calculator answers a very specific question: how to calculate the birth date from the age at death. From time to time, this information is unique and fundamental data in genealogy research. Our tool can help you recreate your genealogical tree or help you discover more about the life of people from our past. Keep reading this article to learn:

  • How to calculate the birth date from the death date by hand;
  • How to use our birth calculator from age at death to find an exact answer to the same question;

and much more!

How to calculate the birth date from the death date and the age at death

Calculating the birth date from the age at death is a simple task, but it depends on the data you know.

  • If you know only the age in years, you can approximate the birth year.
  • If you know the age in years and months, you can expand this information on the date of birth but keep some inaccuracy (the result may be shifted by one month).
  • If you know the age in days, you can obtain the most accurate result (applying the proper algorithm).
  • Knowing the age in the format years/months/days can give you similarly accurate results, but with some catches.

We are going to deal mainly with the two latter cases.

Calculate the birth date from the death date and the age in days

There are two ways you can do this:

  • Convert the date of death to Julian day, and subtract the age in days to find the Julian day of the birth date. The inverse conversion, however, is cumbersome and not easy to do by hand.

  • Separate the age in days into three parts:

    • Days in the year of birth;
    • Days in the full years;
    • Days in the year of death.

    And follow the next steps:

    1. From the date of death, calculate how many days that person lived in the last year. You can approximate the result by multiplying the number of months by 30.430.4, the average month length.
    2. Subtract this result from the age in days.
    3. Find the number of years lived by dividing the last result by 365.25365.25 and rounding down the result.
    4. Subtracting the number of days in the full years plus the number of days in the last year from the age in days gives us the number of days lived in the first year. We can convert this quantity back to date by dividing it by 30.430.4 and rounding down the result to find the number of months. You then have to subtract this result from 12 to find the birth month. Subtract the remainder from 3030 (or 3131, or 2828: it depends) to find the birthday.

So many approximations likely cause the result to be slightly off: however, you'd be in the correct month!

Calculate the birth date from the death date with age expressed in years, months, and days

This second way requires you to perform multiple subtractions:

  1. Subtract the number of days of the age from the one of the death date. Carry over 30.430.4 if the subtraction gives a negative result.
  2. Subtract the number of months in the same fashion. Eventually, carry over 1212 from the years.
  3. Subtract the years to find the year of birth.

As for the methods above, we are introducing some small approximations that can make your result inaccurate. The best option, if available, is to use an online calculator with a calendar to calculating this difference for you!

Other age and birth date realted calculators

If you are interested in birthdays, ages, and genealogy, our tools will be perfect for all your needs. Try our:

FAQ

How do I calculate the birth date from the date of death?

If you know the age in the format years/months/days, you can calculate the date of birth from the date of death with three simple subtractions:

  1. Subtract the number of days in the age from the death date's days.
  2. Subtract the number of months between the two dates.
  3. Subtract the years between the two dates.

You may have to carry over and tune the quantities in the subtractions: remember that a month has, on average, 30.4 days, and a year has exactly 12 months.

What is the birth date of Queen Elizabeth II?

We know the age of the Queen, 96 years, 4 months, and 18 days. Her death happened on the 8th September 2022. We perform these three subtractions to find her birth date:

  • For the days (carrying over from the months): (8 + 30.4) - 18 = 20.4.
  • For the months (adjusting the values): (9 - 1) - 4 = 4.
  • For the years: 2022 - 96 = 1926

Queen Elizabeth's birth date is either the 20th or the 21st April 1926. The recorded one is the latter: we must round up our result!

Can I find the date of birth from the age in years?

No, not exactly. If you know only the age in years, you can only find an approximate birth date. To do so, subtract the age in years from the year of death. The result can be one year higher than expected if the birthday of the person you are considering hadn't happened at the time of death.

Davide Borchia
Death date
Age
yrs
Date of birth
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