JavaScript Birthdate Calculator

Calculates birthdate from death date and age of death in day/month/year format. This web page can be saved to your local hard drive and used without connecting to the net. Just choose Save As... from the File menu.

Assumes New Year on Jan. 1.

This new version can use two different computation methods: (the 28-day-month calculation has been removed due to some problems with the logic and its general uselessness)

  1. 30-day fixed-length months (the "8870" system is a variant of this)
  2. Calendar-length months

Please see my explanation of birthdate calculation methods, and keep in mind that due to uncertainty as to which calculation method was originally used and due to possible errors in the original calculation, calculated dates should be considered to be accurate only to within a few days unless you have good reason to be more confident in them. It is not unusual to encounter original calculation errors as large as 1 month, so beware!

This JavaScript utility uses tables, the forms interface, and of course JavaScript. JavaScript is supported by most browsers today, though some very old browsers, such as Netscape 1.0, don't support it.

Please report any problems to Ben Buckner, but first make sure you're not just reading something wrong.


Month Length:

Enter date of death and age at death:


To perform your calculation, click on this button: .

This has been yet another web page by Ben Buckner.

See these links for calculating YMD ages and DMY ages