Date Calculator - Macintosh Software for Genealogists

The Date Calculator is a MacOS X application for many date and time calculations useful to genealogists. It is free if you are a registered user of GEDitCOM II. For others you can get it at the Map App store.

The Date Calculator has the following capabilities and more:

You can enter dates a wide variety of ways and convert the dates between four different calendars. The Date Calculator supports the Gregorian, Julian, Hebrew, and French Republic calendars.
You can customize the format for display of dates.
You can calculate the day of the week for any precise date.
You can enter two dates and calculate the time span between those two dates.
You can enter any time span and add or subtract it to or from the date.
You can add or subtract time spans.
Most date applications expect you to enter precise dates with a day, a month, and a year before they will do conversions or calculations. All features of the Date Calculator can be done on "fuzzy" dates. "Fuzzy" dates are dates with just a month and year or just a year.
When time spans are calculated between fuzzy dates, the Date Calculator will calculate the maximum and minimum times between those dates and report it as a time range.
When times or time ranges are added or subtracted to or from fuzzy dates, the Date Calculator will calculate the range of possible dates.
Fuzzy date calculations are often useful to genealogists. For example, if you know someone was born in 1824 and died in NOV 1901, how old was he at death? Using the Date Calculator, you can find the time span between those dates to determine he was "BET 76y, 10m, 2d AND 77y, 10m, 30d". Thus, he was 76 or 77 years old with a greater chance of being 77.
Adding or subtracting time spans to or from fuzzy dates can also be useful. For example, if you know someone died in NOV 1901 at age 77, when was she born? Using the Date Calculator, you can subtract "BET 77y AND 77y, 364d" from "NOV 1901" and find the possible birth dates as "BET 3 NOV 1823 AND 30 NOV 1824". If you later find out they were born in 1824, then the birth date is narrowed down to NOV 1824 or DEC 1824.
Extensive help information with details about each of the four supported calendars is included.

Acknolwedgement: Date Calculator uses the date conversion utilities written by Scott E. Lee. He has written a Date Convertor Web Site that converts precise dates between Gregorian, Julian, and Hebrew calendars. He has also posted an excellent Calendar Overview about those calendars. Most of his overview is included (with permission) in the Date Calculator help.

Purchase

If you are a registered user of GEDitCOM II the lastest version of Date Calculator is included in your download of GEDitCOM II. For those not registered for GEDitCOM II, Date Calculator is available as a standalone app for download and purchase from the Map App store. The current version is 3.1 (as of February 2024).

Contact

Author: John A. Nairn
Email: john@geditcom.com
Privacy Policy

Other software by the same author:

GEDitCOM II — Genealogy software for the Macintosh.
PublishPlot — Easily create publication-quality plots for scientific journals, other publications, or just because you want nice-looking plots.
Computational Mechanics Software — material point method (MPM) and finite element analysis (FEA) software.