You'll be shown random dates one at a time. Name the day of the week as fast as you can. The timer runs from the moment each date appears.
Tracks which year endings slow you down or trip you up most. Needs 2+ correct answers to appear in the time card.
Century code + Year code combined. Add your month code + day number, then mod 7 for the day of the week. ★ = current year
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Enter any year and find its Doomsday — the day of the week that all Doomsday anchor dates fall on.
Conway's method finds the day of the week for any date by anchoring to Doomsday — a set of easy-to-remember dates that always land on the same weekday within any given year. Master the anchor dates first, then learn to calculate which weekday Doomsday falls on for any year.
These dates always fall on that year's Doomsday, no matter the year. Memorize them and you can always find a nearby foothold in any month.
The last day of every even month is a Doomsday.
The last day of February — 28th normally, 29th on a leap year.
March 14 (Pi Day 3/14) and September 5 (9-to-5 at 7-Eleven).
Jan 3 in normal years, Jan 4 in leap years.
The 1900s anchor is Wednesday (3). For any year in the 1900s, take the last 2 digits of the year and apply this formula:
a = ⌊y ÷ 12⌋
b = y mod 12
c = ⌊b ÷ 4⌋
Doomsday = (3 + a + b + c) mod 7
Example — 1985: y=85, a=⌊85/12⌋=7, b=85 mod 12=1, c=⌊1/4⌋=0 → (3+7+1+0) mod 7 = 11 mod 7 = 4 = Thursday
Replace the fixed 1900s anchor (3) with the century anchor for the year in question. The pattern repeats every 400 years.
Example — July 4, 1776: Century anchor for 1700s = 0. y=76, a=⌊76/12⌋=6, b=76 mod 12=4, c=⌊4/4⌋=1 → (0+6+4+1) mod 7 = 11 mod 7 = 4 = Thursday. Nearest Doomsday in July = 7/11. July 4 is 7 days before July 11 → Thursday − 7 = Thursday. ✓