I have built this to properly learn and apply the Doomsday algorithm (John Conway's method for working out the day of the week for any date in your head). Many years ago I read about the doomsday algorithm and I kind of learned it. It took many hours for me to get to a point where I would occasionally right. And it was slow, like a minute per solve.

Now I've built this Free-to-use site to help me practice and get my accuracy up and my solve times down. I'm solving most dates in 3-5 seconds through just "playing" here for a few minutes each day.

The stats here are clear: everyone who's spending time on these mini games and just practicing solving dates get much better and faster at it.

Reading about, and understanding the algorithm is fairly easy, getting fast enough to actually do it live is quite hard, and that's really a practice problem. So this site is built around drilling. There are 10+ mini games to play with increasing complexity to learning the various calculation steps, but more crucially practicing getting fast at solving them.

There's a main game with a few different modes where you're presented a random date and you pick the weekday you've calculated for it. The site gives you all sorts of stats for you to dive into to understand your accuracy and speed progression.

You can try it with no signup. Log in to track progress and unlock a few extras.