Doomsday Method: what day was it? Learn to know instantly.

What day was it? Learn to know instantly. July 20, 1969: Sunday, solved in 3.4 seconds, next to the Doomsday home screen.

Someone names a date, you name its weekday in seconds, with no calendar.

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The trick that makes it possible

Every year, 4/4, 6/6, 8/8, 10/10 and 12/12 share one weekday: the year's doomsday. Learn one weekday, and you have the whole year.

Guess the weekday of any date. What day was July 20, 1969? Sunday, solved in 3.4 seconds. It's not a guess. It's a trick. Just 4 steps, the same for every date: century, year, month, count. Learn the trick step by step. Chapter 1 done! No math degree needed. Drill the part you're slow at. Five stars! Counting in sevens, nailed. Compete with everyone. Win the day! Crowns for daily winners. Watch your rating climb. +205 this week! Rating up to 1,484. Offline. No ads. No account. Free to start! Pro is a one-time unlock.

The Doomsday algorithm in four steps

Steps 1 and 2 give you the year's doomsday. Steps 3 and 4 turn it into the answer. For a date this year, start at step 3.

  1. Century anchor

    One weekday per century. The pattern repeats every 400 years.

  2. Year offset

    A number from 0 to 6, from the last two digits of the year.

  3. Month doomsday

    One easy date in every month that always falls on the doomsday.

  4. Count

    Jump to your date in sevens, then add or take away a few days.

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Frequently asked

Anything else? Get in touch.

Who invented the Doomsday method?

John Horton Conway, in 1973. He built on a method Lewis Carroll published in 1887.

How long does it take to learn?

Dates in the current year take about an afternoon. For the 1900s and 2000s, give it a couple of weeks of short daily practice.

Do I need a good memory?

No. It comes down to about a dozen facts and some simple adding and subtracting.

Does it work for any year?

Yes, for the Gregorian calendar. Dates before a country switched calendars, like Britain before 1752, need a Julian adjustment. The app teaches it.

Is the app free?

You can start for free, with the first 16 lessons. A one-time Pro purchase unlocks everything. There is no subscription.

Doomsday Method app icon

Give it an afternoon.

The first 16 lessons are free.

  • Learn

    48 lessons in 11 chapters. Each one ends with a question.

  • Train

    Ten drills, one for every step, plus Julian dates and Easter.

  • Play

    Classic, a Daily Challenge and Time Attack, with Game Center leaderboards.

No account, no ads. Analytics only if you say yes. Pro is a one-time unlock.

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Doomsday Method Name the weekday of any date, in your head.

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