You must have seen several talent-shows where people would guess the day of a given dates. Some of you must have thought they do it by memorizing the entire calendar. Well, it somewhat does require memorizing, not the entire calendar though, and the rest is basic calculation. Let’s jump right into it.

 The method that we are gonna discuss about is called Doomsday Rule. This algorithm was devised by John Conway, inspired by Lewis Carroll’s perpetual calendar algorithm, in the year 1973. By using this method anyone can calculate the day of any date in any given year.

In this method one need to remember these special dates also known as doomsday, these days include:

4/4,6/6,8/8,10/10, 12/12, 7/11,11/7, 9/5,5/9

[ Note- Every dates in this article are in the format of month/day/year]

The date for the month of January and February differs according to the leap year.

The special dates of January are the 3rd and 4th (for leap year) and for February, it is 28th and 29th (leap year). So, it is 1/3 and 2/28 for three years and ¼ and 2/29 the other.

For March, the special date is the pi day, that is, 3/14.

Other notable special dates are 10/31- Halloween and 12/26- boxing day.

Now, one may ask what’s special about these dates, to that, these days in a given year appears on the same day. For example, if you know the 12/12 is Friday, then the rest of the dates mentioned will also be on Fridays.

Now that we know the trick let’s learn about how to apply them. For example, let’s find out the day of 11/26/2023.

For every question we need a reference date, which could be any of the doomsday. For this case let’s take the pi day as the reference. Once we know about pi day we will automatically know about the rest of the days. And that’s when we face the question that how do we know that. There is a simple trick to that as well. All you need to remember is that the pi day was a Tuesday in the year 2000.

2000 - Tuesday

2001- Wednesday

2002- Thursday

2003- Friday

2004- Sunday

As you can see, that every year the day increments by one and in the leap year it is incremented by 2.

When you need to find out about past dates, those of before 2000, all you need to remember is this pattern,

1700- Sunday

1800- Friday

1900- Wednesday

2000- Tuesday

And this pattern repeats, which means 2100 pi day would be on Sunday, 2200 on Friday and so on.

Now let’s get back to the question. So, the year is 2023. We know on 2000 pi day was in Tuesday, all we gotta do is add the number of years plus the number of leap years to Tuesday,

Tuesday + 23 + 23/4(=no. of leap years)

Tuesday + 23 + 5 (ignoring the decimal, which is to be done in every case, since years can’t be in decimal)

Tuesday + 28= Tuesday (*since 28 is a multiple of 7)

(*when days are added with numbers which 7 or multiple of 7, you would get the same day)

So, pi day in 2023 is a Tuesday. After this step you need to find the nearest doomsday to the date in question. Here, it would be 11/7. 11/7 is also Tuesday. To find 11/26 we gotta add

Tuesday + (26-7) = Tuesday + 19 = Sunday

Hence 11/29/2023 will be a Sunday.

You can go to the calendar and check if the results are correct. You can try this method on any date and year and see it for yourself.

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