On what day of the week were you born?

Ever wondered what day of the week it was when you were born into this lovely planet we called Earth? Ever wondered what day of the week your 21st birthday will be so that you can plan the most awesome birthday party of the year? Ever simply wondered what day it is on let's say the 12th of March, in the year 4567 i.e. the date that will be read as 12-3-4567. Will you need to slowly count day by day from the year you are in now until the year 4567, or is there some short cut to all of this tedious looking and mundane calculations?

Now, let me share with you six easy steps to find out the day of the week of a particular date! We shall use 17 Jan 1942 as an example for our explanation.

Step 1: What is the date? 17

Step 2: What is the month? January. Then January is 6. Why?

A number is assigned to each of the twelve months. The assigned number is based on a formula which we will talk about later in the blog post. The table below shows what number is assigned to which month.

Step 3: We need to offset the decade? As the year is 1942, to offset will be 2. The decade offset from the year 1900 to 2010 can be found from the table below.

Step 4: What is the last digit of the year? 2.

Step 5: We need to offset leap years. For example, 1942 appears in an even decade (since 4 is even). The table below then tells us that the leap year offset for 1942 is 0 (look under the "2" column in the "even" row.)

Step 6: Add everything in red above from Step 1 to Step 5 will give you 27. Take 27 and divide it by 7 and find the remainder, which will then be 6.

6 = Saturday and you have your answer of which day of the week is this date!

To summarise, please refer to the following diagram:

(Source: Plus Maths - What Day Of The Week Were You Born?)

Sadly, the method above can only help you calculate until the year 2010 due to the restriction in Step 3. So how are we to find out the day of the week for dates after 2010?

Introducing the Zeller's congruence!

(Source: Wikipedia)

h is the day of the week (0 = Saturday, 1 = Sunday, 2 = Monday, ...., 6 = Friday)

q is the day of the month

m is the month (3 = March, 4 = April, ..., 14 = February)

K is the year of the century (year mod 100)

J is the zero-based century 

Now, for those of you who understand everything about this formula may find out the day of the week easily using it.

On the other hand, there must be a lot of you who find that you do not understand the formula at all. Your brain is now going haywire from reading all of this unknown words and gibberish...Oh no!!

Fret not, as here comes the joys of internet. Simply click HERE and the website that you go to will help you find the day of the week within a split second! Now you can start planning for your future birthdays that fall on weekends and have the time of your life!

Sadly, the above formula and the website uses Zeller's congruence, which works only from years 1582 to 4902. If you try any year not in between the two years mentioned, the answer will NOT be accurate. That said, if you are as brilliant as Zeller, why not start a research in this area? Perhaps you will be the next person to come up with a formula that can calculate the day of the week for years before 1582 and after 4902!