- the last day of February (this is the key fact if you remember nothing else. Doomsday is always the last day in February for every year.)
- 4/4, 6/6, 8/8, 10/10, and 12/12
- 5/9 and 9/5
- 7/11 and 11/7
- March 7 (7 days after the last day of February)
- January 3, except for leap years (years divisible by 4), when it’s January 4
It’s easy to remember Doomsday for the even months. To remember the day for the odd months, use the mnemonic, “I work 9-to-5 at the 7-11.”
Isn’t it wonderful knowing stuff like this? I can never know enough fun stuff like this. I don’t remember where or when I first stumbled across the Doomsday algorithm, but I have always enjoyed it and it’s quite handy when someone asks “what day does September 24th fall on?” So…
- For 2014, Doomsday is always on Friday.
- Doomsday is therefore on Friday, September 5th.
- Add 21 to get September 26th (multiples of 7 make the addition easy).
- September 24th is Wednesday.
A bit of mental math never hurt anyone. That said, I have not gone down the rabbit hole of learning all the rules of the algorithm so that I can mentally compute the day for any given date. Whilst I appreciate that it would make my mind a little more nimble mathematically, I prefer the lazy man’s way of simply looking at a calendar.
However, there are no shortage of sites where you can learn the full algorithm if you want. My favorite site for the algorithm includes lots of background information and additional resources. But maybe you need your hand held till you build up your confidence (and there’s no shame in having your hand held). In that case, use timeanddate.com’s remarkably well-hidden Doomsday Calculator. which steps you through each calculation till you can learn it by heart. Click the “Show/hide all steps” link to see all the steps on one page.
As for me, I will continue to check each new year’s calendar for the last day of February and start my calculations from there.