FIND THE DAY OF THE DATE

Here are some shortcuts/tips to find out the day of the week from the given date. You can play these trick as instructed, with your parents or friends and prove your talent to them.

Day of the Date

Finding Numbers of Months

Century offset calculation (Gregorian Calendar):
Step1 :Take the first two digit of the given year.
Step2 :Calculate the next highest multiple of 4 for the first two digit number.
Step3 :Subtract 1 from the number.
Step4 :Then, subtract the first two digit of the given year
Step5 :Finally, multiply the resultant value with 2.

Example:

Calculate centruy offset for 1900s century.
Let us take the first two digit 19.
The next highest multiple of 4 for the first two digit number 19 is 20.
Subtract 1 from the number. i.e. 20-1
Subtract the first two digit of the given numberi.e ((20-1)-19)
Finally, multiply the resultant value with 2..
1900s = ((20-1)-19)*2 = 0.
Below given Gregorian Century Offsets table shows the other century and offset values,

Century	Offset
300, 700, 1100, 1500,1900, etc.	0
400, 800, 1200, 1600, 2000, etc.	6
100, 500, 900, 1300, 1700, etc.	4
200, 600, 1000, 1400, 1800, etc.	2

Find the Month Offset:
Consider there are 4 weeks in a month, which means 4x7=28days. January has 31 days. The days remaining are 31-28=3. The reminder helps you in calculating the numbers for each month.
Initially, Take Jan as 0
February = ( Number of days in Jan + Remaining days in Jan ) / 7) = (31+0)/7 = 3
March = ( Number of days in Feb + Remaining days in Feb ) / 7) = (28+3)/7 = 3
April = ( Number of days in Mar + Remaining days in Mar ) / 7) = (31+3)/7 = 6
Continue the same process till December... The numbers for the months are,

Month Offsets table:

Month	Offset
January	0
February	3
March	3
April	6
May	1
June	4
July	6
August	2
September	5
October	0
November	3
December	5

Numbers for the weekdays are,

Sunday	0
Monday	1
Tuesday	2
Wednesday	3
Thursday	4
Friday	5
Saturday	6

You are about to remember this table before proceeding with the trick.
Now let us play the trick

Remember the formula Century offset + Year offset + Month offset + Day Offset
Where,

Day Offset = Given day mod 7
Year Offset = ( Last two digit of year + (Last two digit of year / 4) ) mod 7
if the given year is leap year and month is Jan/Feb, thenYear Offset = ( ( Last two digit of year + (Last two digit of year / 4) ) mod 7 ) - 1
Step1: Ask for any specific date and challenge them you could tell the weekday of the date mentioned without any calculation. Example: 23^rd June 1986
Step2: Take the century offset from the first table, 1900 is 0.
Step3: Calculate the year offset for 86 is ((86 + 86/4) mod 7) = 2
Step4: Take the month offset from the second table, June is 4.
Step5: Calculate the day offset, that is 23 mod 7 = 2
Step6: Now add all the 4 numbers: 0 + 2 + 4 + 2 = 8.
Step7: Divide 8 by 7 = 1 remainder 1.
The reminder tells you the day. 

Answer: Monday

Source - https://www.easycalculation.com/funny/shortcuts/day.php