Doomsday Trainer
Know the day for any date!
Free · Designed for iPad. Not verified for macOS.
Master the Doomsday Algorithm — calculate the day of the week for any date in history in seconds.
PLAY
Build your streak and beat the clock. Every correct answer adds to your streak; one wrong answer ends it. Compete on the global leaderboard for Longest Streak and Fastest Average Speed.
BATTLE
Challenge a real opponent to a live 1-on-1 race. Five dates, fastest and most accurate player wins. Elo-based ranking tracks your competitive record.
TRAIN
Six methods to choose from:
• Doomsday — the classic anchor-day approach
• Odd + 11 — the Fong-Walters mental shortcut
• The Wollin Shortcut — a memory-based system using vectorized doomsdays, the Square Knot Rule, and the Wollin Calamity Table (by u/Nillows)
• Conway's Method — the original algorithm by John Conway
• Mod 28 — reduce any year to under 28 before calculating
• Custom Mode — pick your own date range, century, or decade
DRILL
Targeted practice for each component: months, centuries, years, mod 7 arithmetic, and the full Wollin Shortcut drill suite.
TUTORIAL
New to the algorithm? The built-in tutorial walks you through everything step by step.
Ratings & Reviews
Various bug fixes and game mode improvements!
The developer, Maarten Claessen, 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:
- User Content
- Identifiers
Accessibility
The developer has not yet indicated which accessibility features this app supports. Learn More
Information
- Seller
- Maarten Claessen
- Size
- 15.8 MB
- Category
- Education
- Compatibility
Requires iOS 15.0 or later.
- iPhone
Requires iOS 15.0 or later. - iPad
Requires iPadOS 15.0 or later. - iPod touch
Requires iOS 15.0 or later. - Mac
Requires macOS 12.0 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+
- Copyright
- © 2026 Maarten Claessen
