Disclaimer : I found this method on YouTube; I merely wrote it down for convenience (so I can make a program someday) and thought I should share it with you all.
Here's the source : Video Link
Let Sunday = 0, Monday = 1 .... Saturday = 6
Doomsdays -
The day shared by specific dates (day changes by year, dates remain same)
Jan/3(4th in Leap), Feb/28th (29th in leap), Mar/14th, Apr/4th ... can be written as
1/3(4), 2/28(29), 3/14, 4/4, 5/9, 6/6, 7/11, 8/8, 9/5, 10/10, 11/7, 12/12
For even months, it's same date as the month (expect Feb) For Feb it's the last day (29 or 28 depending on leap or not) For odd months : working 9/5 on 7/11 (reverse holds true), Pie 3/14, Jan is 3rd or 4th (Leap)
Eg : 2018's doomsdays are all Wednesdays
Century Code -
In gregorian calendar, dates repeat every 400 years. so only 4 century codes possible/required
... 1500 1600 1700 1800 1900 2000 2100 2200 2300 2400 2500 2600 ...
3(Wed) 2(Tue) 0(Sun) 5(Fri)
Eg : 2000's doomsday = Tuesday => 2000's code = 2
Input = dd/mm/yyyy
-> Variable assignment : Quotient (A) + Remainder (B) means A = Quotient and B = Remainder
-> These variables represent fingers on the hand (for manual calculations) : I = Index, M = Middle, R = Ring, L = Little, T = Thumb
-> All calculations involve whole numbers only
-> D stands for Doomsday; so named by the inventor of this method John H Conway
-> For more (visual) explanation, please refer to the video
Eg 1 : Day on 6th Dec 2030
Eg 2 : Day on 23rd Sept 1105