The Doomsday method
A mental shortcut to find the weekday for any Gregorian date. Named after “Doomsday” anchor dates in each year that share the same weekday.
Weekday numbers (this app)
Same as JavaScript getUTCDay(): Sunday = 0 through Saturday = 6. The main trainer and stats use these values.
Sun
0
Mon
1
Tue
2
Wed
3
Thu
4
Fri
5
Sat
6
Quick drill
Mode
Streak 0
What number is Monday?
Tip: keys 0–6 choose a number in name → number mode.
This year (2026)
The last day of February is February 28, 2026, a Saturday. That weekday is this year’s Doomsday—every anchor below falls on it.
Monthly anchors
Memorize these calendar dates; each matches the year’s Doomsday weekday.
- January3rd in leap years, 4th otherwise (same weekday as last Feb)
- Februarylast day (28 or 29) is Doomsday
- March7th ("0 March")
- April4th
- May9th
- June6th
- July11th
- August8th
- September5th
- October10th
- November7th
- December12th
Year and century
- Century anchor: Gregorian centuries have a fixed weekday anchor (often learned as a small table, e.g. 1900 → Wednesday, 2000 → Tuesday). Memorize the entries for the year ranges you practice.
- Year within century: Count leap years and use the “+12 years, −1 weekday” (or similar) shortcut from a reference you memorize, then combine with the century anchor to get that year’s Doomsday.
- Target date: From the nearest anchor in that month, step by sevens to your date and read off the weekday.
Full detail and variants: Doomsday rule (Wikipedia).