Doomsday Method | Mental Game
Master an Extraordinary Skill
Only for iPhone
Free · In‑App Purchases · Designed for iPhone. Not verified for macOS.
iPhone
Someone tells you the date they were born. You tell them it was a Monday.
That is a real skill, it takes about a week to learn, and this app teaches it end to end.
The Doomsday algorithm — invented by the mathematician John Conway — turns any date into its weekday using arithmetic small enough to finish while someone is still saying the date. No lookup. No phone. No calendar.
LEARN
48 lessons across 11 chapters, in three parts
178 checkpoint questions. You answer in your head, then check yourself against the worked reasoning — nothing is graded, and nothing is rushed
Interactive calendars, anchor tables and step-by-step walkthroughs inside the lessons themselves
Mnemonics that stick: 4/4, 6/6, 8/8, 10/10, 12/12, and "9-to-5 at the 7-Eleven"
Six different ways to work the year offset. Pick the one your head likes, and every worked explanation in the app is rewritten in it
Seven Extras: why the method works, Easter and the computus, the Julian calendar, Conway's own shortcuts, the record holders, and full reference tables
A cheatsheet with every anchor and every offset on one screen
TRAIN
10 drills: weekday numbers, counting in sevens, leap years, century anchors, the year offset, month doomsdays, day counting, reverse dates, Julian dates and Easter
Five stars a drill, earned by answering cleanly — right, and inside that drill's target time
Nothing cuts you off mid-question, and training never costs you rating
PLAY
Classic — endless real dates, at your own pace, with no clock at all
Daily Challenge — five dates drawn from the day itself, identical for every player on earth, one attempt a day
Time Attack — two minutes, as many dates as you can, ten seconds off for every miss
Choose your range: 2000–2099, 1800–2199, or the whole Gregorian calendar from 1583 to 2599
YOUR PROGRESS
A Doomsday Rating that rises when you are right and quick, and never pays for a guess
Accuracy and speed over time, your rating history, and a 12-week activity calendar
Game Center leaderboards for today's challenge and the global rating, friends included
BUILT PROPERLY
No account, no sign-up, no ads
Works offline
Every number in every lesson is re-derived by a checker that shares no code with the app, so an explanation cannot drift from the answer it gives
Analytics are opt-in, pseudonymous and on EU servers. You are asked once, and can change your mind any time in Settings
Coming from the old Doomsday Method? Your history is imported and replayed answer by answer, so your chart reaches back and your rating arrives honest
Start free. One optional purchase opens the rest — one payment, not a subscription.
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EULA: https://www.apple.com/legal/internet-services/itunes/dev/stdeula/
Thank you for using the Doomsday Method App to learn and play Conway's famous mental math method!
What's new in 2.1.1:
- smaller bug fixes
The developer, Leon Grimmeisen, indicated that the app’s privacy practices may include handling of data as described below. For more information, see the developer’s privacy policy .
Data Not Linked to You
The following data may be collected but it is not linked to your identity:
- Purchases
- Identifiers
- Usage Data
Accessibility
The developer has not yet indicated which accessibility features this app supports. Learn More
Information
- Seller
- Leon Grimmeisen
- Size
- 11.1 MB
- Category
- Education
- Compatibility
Requires iOS 17.0 or later.
- iPhone
Requires iOS 17.0 or later. - Mac
Requires macOS 14.0 or later and a Mac with Apple M1 chip or later. - Apple Vision
Requires visionOS 1.0 or later.
- iPhone
- Languages
- English
- Age Rating
4+
- 4+
- In-App Purchases
Yes
- Doomsday Pro $9.99
- Copyright
- © 2026 Leon Grimmeisen
