Birth From Death Date Calculator
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:
 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 $30.4$, the average month length.
 Subtract this result from the age in days.
 Find the number of years lived by dividing the last result by $365.25$ and rounding down the result.
 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 $30.4$ 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 $30$ (or $31$, or $28$: 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:
 Subtract the number of days of the age from the one of the death date. Carry over $30.4$ if the subtraction gives a negative result.
 Subtract the number of months in the same fashion. Eventually, carry over $12$ from the years.
 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 related 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:
 Subtract the number of days in the age from the death date's days.
 Subtract the number of months between the two dates.
 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 8^{th} 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 20^{th} or the 21^{st} 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.