Tennessee Genealogical Society

taken from the Jacksonville Area Genealogical and Historical Society, November 1, 1985

1. Set down death-year, month and day expressed in numbers, as example below:

    Death date: 20 August 1973        1973    8    20

    Birth date: 10 June 1901            -1901   -6  -10   

                                                      72 ys  2 mo 10 ds

2. To "borrow days" when numbers are unequal: The formula is 1 month-30days.

                                                                   7

    Death date: 10 August 1973        1973    8  +10 = 40 ds

    Birth date: 20 June 1901            -1901   -6  -20

                                                        72 ys 1 mo 20 ds

3. To "borrow a month". The formula: 1 year = 12 months.

                                                              2    12mo

    Death date:  20 August 1973        1973    +8 = 20 mo    20 ds

    Birth date:    10 Sept. 1901          -1901            -9 mo    10ds       

                                                        71 ys              11mo    30ds

Given a death date and yr-mo-da, one can reverse the process to find the approximate birth date. The formula is: 12 months x 30 days = 360 days.

This will not give exact date of birth, because we actually have 365 days per year, except leap years. However, this methods of birth determination would give a date within 5 days of actual birth, by which one could look for birth records, etc.