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Date calculator

This is a very simple date calculator that I made in a single afternoon (and some nighttime too I guess) on June 4th 2025 based on the XKCD calculator engine I made a few months earlier. Some considerations:

Dates are input in the year-month-day format;
Dates before year 1 use negative numbers (5 BC would be year -4);
This uses the proleptic Gregorian calendar.

The source code is available here: script.js.

Also! Default values are dates/numbers that I really like referencing for whatever reason. Two are from webshows, one is a "mind inside joke" and the other is from a conworld. Enjoy!

Calculators

Day addition

Date:
Days to add:

Date difference

Date 1:
Date 2:

Date to ordinal

Date:

Ordinal to date

Ordinal:

< Date calculator