 How To Calculate The Day Of The Week

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ELREY'S REVISED METHOD

Century number
16 = 0
17 = 5
18 = 3
19 = 1
20 = 0
21 = 5

Month number
144025036146
JFMAMJJASOND

1234560      -  Day of week number (the remainder when divided by 7 )
SSMTWTF      -  Day of week

Formula:   ( Month number   + day  + Century number + year + year / 4 )  mod 7 =>  day of week number
|                          |                                               |
v                          v                                               v
144025036146               16 = 0                                            1234560
JFMAMJJASOND               17 = 5                                            SSMTWTF
18 = 3
19 = 1
20 = 0

• If Leap year and Jan or Feb, minus 1. (previous day)

• mod means 'remainder when divided by ...'

• Example July 18, 1990

July   28     19    90     1/4 of 90
(   0  + 28 +    1 +  90  +    22        ) mod 7  =
(                141                     ) mod 7  = 1  (Sat)

• May 27, 2015

May     27      20      15    1/4 of 15
(  2  +  27   +   0  +   15 +   3           )  mod 7 =    5  (Wed)

• May 8, 2015

May      8     20      15    1/4 of 15
(  2  +   8   +  0  +   15 +      3        )  mod 7 =    0  (Fri)

• Sep 18, 2016

Sep   18    20    16      1/4th of 16
( 6  + 18  +  0  + 16 +       4        ) mod 7 =  2 (Sunday)

• Jan 31, 1883

Jan      31    18     83
( 1  +    31 +   3  + 83  +  20  ) mod 7 =
138        mod 7 =  5 (Wed)