The one-page calendar that changes how you view the year | by Ethan Siegel | Starts With A Bang! | Jan, 2025

It’s simpler, more compact, and reusable from year-to-year in a way that no other calendar is. Here’s both how it works and how to use it.

Each year, most of us throw out our old calendar and replace it with a new one. Each month, we flip our calendar forward another page, and if we ever need to know which day-of-the-week corresponds to a particular day/month combination, we have to either calculate it ourselves or flip forward/backward to the relevant month. Simple but curious questions, such as:

• What date will American Thanksgiving fall on this year?
• Which months have a “Friday, the 13th” in them?
• What day of the week does July 4th fall on?
• Or which day of the week is Christmas Day?

aren’t so easy to figure out unless you actually flip to the needed month (or look up all of the months) to figure out what the proper answer is.

But it turns out that, mathematically, the answer to these questions — or any question where you want to match up the day of the week with the day/month combination in a year — are extremely predictable, straightforward, and simple to figure out. If, that is, you don’t restrict…