a3Genealogy - Accurate, Accessible Answers - specializes in military, naturalization records, Native American and African American ancestry. The a3Gen blog is penned by Kathleen Brandt, an international genealogy consultant, speaker and writer. a3Gen clients span from Europe, Asia and Africa to the Americas.
Basic math can help even genealogist. Let’s take a walk through the cemetery armed with only a birth date, and without your beloved calculator. And VOILA, you finally find Mrs. Ancestor’s tombstone! Mrs. Ancestor’s grave marker (or death record) reveals important information. She died at 83y, 11m,29d on 28 March 1901 (I’ve found my share of these types of etchings).
Very basic math would place Mrs. Ancestor birth year as 1818 (1901 minus 83years). But we have more information on Mrs. Ancestor now. Ignoring the reason her loved ones declared it important to put 83y 11m 29d on her tombstone; this added information has helped me break a few cases. Armed with the 8870 formula, I can determine an exact birth date.
Let’s use the 8870 formula on the spot, at the tombstone, without a calculator to quickly derive at the answer. There’s no need to count backwards. This method can also be used to verify the accuracy of your birth data, or may create questions if the birth year you have the one calculated by the 8870 formula is correct.
Apply the Formula*
Tombstone Facts on Mrs. Ancestor
Died: March 28, 1901
Age on Tombstone: 83y 11m 29d
Birth date: unknown
Death 19010328 March 28, 1901
Age - 831129 83y 11m 29d
- 8870 Constant – 8870 Formula
Birth date 18170329 March 29, 1817
There are times that you will get answers that don't work out perfectly. For example you may get 13 months or 58 days. If this is the case, base the answer on 12 months, 30 day (i.e. 13 = 1 more year; whereas 58 days needs one more month and 28 days (58-30 =28 days).