Although it is well known that Conway was able to quickly calculate the day of the week of any given date, it is less well known that one part of the algorithm is easy to remember and useful in practice: In any given year, the following dates all fall on the same day of the week: 4/4, 6/6, 8/8, 10/10, 12/12, 5/9, 9/5, 7/11, 11/7, and the last day of February. For example, in 2020, all these dates fall on a Saturday. Conway, in his characteristically colorful way, would say that the Doomsday of 2020 is Saturday. Knowing this fact allows you to calculate fairly quickly in your head, with no special training, the day of the week for any date in 2020.

The full algorithm tells you how to calculate the Doomsday of any given year, but in everyday life, one is mostly interested in the current year, so you can just remember this year's Doomsday, and update that fact once a year.