I made a website for teaching you how to calculate the weekday of any past or future date within seconds.

Whattheday.com explains how the Doomsday algorithm, invented by John Conway, works and how you can apply it to convert any date to a weekday. It gives access to mini games for improving your speed and accuracy and keep track of your progress as you learn. It's not easy at first, but by playing these games you will soon have a quirky skill for life.