How to Find a Birth Date from Age at Death

Not every record is straightforward in giving information. Take tombstones and death records, for example. For some reason, many of them don’t list the birth date. Instead, they list the exact age when the person died. Fortunately, it isn’t that hard to find a birth date from the age at death.

Watch the how-to video or keep scrolling to read the tutorial:

Two notes:

  • There are several birth date calculators online. However, if you know the method, you can do it yourself in about the same time it takes to look one up and type in the information.
  • Yes, I know about the 8870 formula. Frankly, I think it overcomplicates things. (Plus, I can never remember the number I’m supposed to subtract.)

Here’s an example using Phineas Ford’s tombstone in Old Colony Burying Ground in Granville, Ohio:

How to Find a Birth Date from Age at Death
Phineas Ford tombstone, Old Colony Burying Ground, Granville, Ohio

Phineas Ford,
April 7, 1839,
64 Y. 5 M. 7D.

That’s age 64 years, 5 months, 7 days.

How to Find the Birth Date:

Step 1: Subtract the Number of Years

Phineas Ford died April 7, 1839. Subtract his age of 64 years.

= April 7, 1775 (1839 – 64 = 1775)

Step 2: Subtract the Months

Take that date and count backward the number of months. April 7, 1775 counting backward 5 months = November 7, 1774.

Note: You do NOT need to know how many days are in each month at this point. Just be sure that you roll back the year if you count back to the previous calendar year (like we did with Phineas.)

Step 3: Subtract the Days

Here is where you need to account for the number of days in a month.

November 7 minus 7 days is October 31.

Answer: Phineas Ford was born 31 October 1774.

See, I told you it wouldn’t be that hard!

A Note About Other Calendars

If you are working with Quaker calendars or with changes between Julian and Gregorian calendars, you will need to take special care in calculating those dates.

Now go forth and calculate those birth dates!


Posted: December 3, 2015.

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  • Thank you for sharing this! I have always calculated dates of birth in this same manner, hoping that the people who figured it out originally and carved it on the stone used the same method I do. 🙂

    • You’re welcome! There are other methods that sometimes results in a date that’s different by a day or two. But I’ve found this method to be the most consistent when I compare the calculated date with a record that does list the birthdate (like when the tombstone lists the age, but the death record lists the birth date). I also think it’s the most “natural” method. If you ask someone what the date was 5 months from today (December 3, 2015), they’d say July 3, 2015. They wouldn’t stop to figure out how many of those months had 30 days in them.

    • Good point. Yes, we should seek documentation pertaining to the person’s birth. However, in some cases, the age at death is the only documentation we have for the person’s birth date.

      • Indeed, and a birthdate calculated from the age and date of death is merely a representation of the gravestone’s claim as to the date of birth. A date that is off may be more helpful than not having a birthdate at all.

        In looking through memorials on Findagrave for headstones of soldiers in a cemetery, when the date of birth was not entered then for most headstones I had to click on all the memorials. If the dates of birth for infants had been added from calculations, I could have saved myself the trouble of having to click on many memorials only to find that they were for people who were only days, months, or a few years of age.

        A calculated date of birth that is off by a small number of days, months, or even years might also help when it comes to Ancestry suggesting matches. If you know a person’s date of birth but not their date of death, and if a memorial on Findagrave has a date of death but not a date of birth, Ancestry is not necessarily going to suggest a connection, or the right match lacking a birth date will not stand out among others when it’s someone with a common name. If the date of birth is added from a calculation, I think Ancestry would make the suggestion, and the connection is more apt to stand out among search results.

        Of course, it would help if genealogical websites offered the opportunity to enter age, and if they automatically calculated a date of birth and identified such a date of birth as calculated rather than explicit on the stone on documented by other records.

  • my great great grandmother was thought to be 107 years old, but looking at marriage license she was younger. Lots of misinformation, about date etc on death certificate. Do not know if her headstone has that info, and if it is still around. There was a flood in Virginia years ago. Great Great Grandfather is buried in Arlington Cemetary. I know when he died so will this method work if you know the death date?

    • You would need to know the age and the death date. However, it’s important to remember that the information is only as good as the knowledge of the person who gave it.

  • Amy,
    Great post! I definitely agree with your methods provided here. This process does appears to be the most natural method at determining a date of birth. Also, an exact or close date of birth can be very beneficial during the research process. I had not used this natural method, but was familiar with the 8870 method. As a cautionary measure, I will note that several years ago I submitted research results to the creator of the birth calculator at, as some people do take the calculated date as gospel, which should not be done with any one source or record. A grave marker or death certificate is secondary information and every source we use should be evaluated using the GPS (Genealogical Proof Standard). I am no expert, but there is some great feedback here a good grasp on the complications of defining a birth date. Thanks for sharing!

    • Thanks for your comments, Tony! Yes, we definitely need to remember that just because the source gives us enough info to calculate the birthdate doesn’t guarantee that the source itself is correct.

    • Well, howdy, neighbor! (Kinda — I’m in Reynoldsburg.) I love Old Colony Burying Ground. I used to stop there sometimes after class at OSU-N.

  • Molly Howard , Coldwater, Mississippi what year was she born ? What year did she pass away? . That’s sharon great grandmother. Ask ann she knows everything, . She lived in Woodstock off of fike rd, with her daughter ophelia. What age was sharon? , her great great grand daughter,? Gladys daughter. Tell me ann and pearl, earleen, queen, earnest priddy.