-- Age Calculator --

This calculator will do four different calculations regarding age. It has two methods of calculating a birthdate, given the date of death and age at death. The first one is more accurate, but the second one, called the 8870 method, which assumes 30-day months, is sometimes better since the age-at-death inscribed on headstones often seems to have been figured on the basis of 30-day months. So if the first one gives you a birthdate like Feb. 31, try the second.

Age at death: Years Months Days

Birthdate: Month Day Year

Date of death: Month Day Year

Result:

Type in a date and this will return the day of the week. Like the calculator above, it should work for anything after Sept. 14, 1752, when the calendar changed from Julian to Gregorian.
Day Month Year

Result:

The algorithm I use for the 8870 method was taken from the website of the Board for Certification of Genealogists. It goes:
• Put the date of death into YYYYMMDD form, padding MM or DD with a leading 0 if necessary.
• Put the age at death into YYMMDD form, padding MM or DD with a leading 0 if necessary. (At this point the BCG website says that if the month is 00, you should change it to 12 and decrement the year by one, but by my math the result is the same, except that it actually throws one of my calculations off.)
• Subtract the age from the date of death, using regular decimal subtraction. If the resulting MM and DD are within normal range for month and day, the calculation is done.
• If the resulting DD came out to either 00 or greater than 30, subtract 70 from it. (This usually amounts to the same thing as adding 30 to the day and decrementing the month by one.)
• If the MM resulting from the last step came out to either 00 or greater than 12, subtract 88 from it. (This usually amounts to the same thing as adding 12 to the month and decrementing the year by one.)
The result will be the date of birth in YYYYMMDD format.