Clocks and Calendars are a regular part of MBA entrance exams. Most of the time, Calendar questions are seen in Quantitative Aptitude section. However, they can also be found in the Data Interpretation Section of CAT papers. What happens if the question asks you to find the day for given date? For example, if the question asks you to find out what day it was on the 6th of August, 1990. What’s the best way to do it quickly?? We will try to answer this question today in this article on Zeller’s Rule. Zeller’s Rule will help us find the day for given date quickly.

## Zeller’s Rule: Find the Day for given Date Quickly

With this technique named after its founder Zeller, you can solve any ‘Dates and Calendars’ problems. Zeller’s Rule can be used to find the day on any particular date in the calendar in the history. All you have to know is the formula given below and how to use it.

Zeller’s Rule Formula

F = K + [(13xM – 1)/5] + D + [D/4] + [C/4] – 2C

where,
1) K = Date. So, for 06/08/1990, we take K=06

In Zellers rule, months start from March.

2) M = Month no.

Remember that month Starts from March in this formula. So,…

March = 1,

April = 2,

May = 3

and so on… till

Dec = 10,

Jan = 11

Feb. = 12

So, for 06/08/1990, M=6

3) D = Last two digits of the year

So, in our example of 6/08/1990 D=90

Also remember that when you have to find day of the first or second month of any year, then Year=Given year-1
i.e. When you want to find Day of 15-2-1990.,
K=15,
Month=12,
D=Given Year-1=1990-1=1989=89 [Thanks Vineet for the Correction]

4) C = The first two digits of century

So, in our example of 06/08/1990.. C = 19.

Let us now calculate the day for 06/08/1990 with the formula above. Remember that the values of K, M, D and C are 06, 06, 90 and 19 respectively.

The formula is F = K + [(13xM – 1)/5] + D + [D/4] + [C/4] – 2C

Replacing the values in the formula, we get

F = 06 + [{(13 x 6)- 1}/5] + 90 + 90/4 + 19/4 – (2 x 19)

Therefore,

F = 06 + 77/5 + 90 + 90/4 + 19/4 – 38

Which gives..

F =06 + 15.4 + 90 + 22.5 + 4.75 – 38

[ We have to Consider only the integral value and ignore the value after decimal. So, the equation changes a bit as shown below. We have just removed value after decimal ]

F =06 + 15 + 90 + 22 + 4 – 38

Therefore, F = 99

Now that you have a numerical value for the day, divide the number by 7. We need the remainder only. For example, in this case, the remainder is 1.

Now, match the remainder with the chart below:

1 = Monday
2 = Tuesday
3 = Wednesday
4 = Thursday
5 = Friday
6 = Saturday
7 = Sunday

Here, 1 represents Monday.

So by Zeller’s rule, 6th of August, 1990 was on a Monday.

Now, Try out some days on your own by CLICKING HERE.

This formula will help you a lot in any Calendar question that you may encounter in Quant or DI. Remember that it is necessary to know the formula properly or else, even a little mistake can render the answer incorrect.

PS: It is natural for all of us to consider January as the first month of the year. However, we request you to please note that March should be treated as first month for using this formula.

With this, you are all set to rock any calendar question that comes in front of you.

Just to reiterate, The most important thing in this concept is to remember the formula as an incorrect interpretation can lead to a false answer.

Best of luck.