RECOMMENDED! Calculation of day of week (28/56/84 method) – Start SpeedCalendar here!

Basic Rules

Rule 1: Year-Month relationship

It is noted that we use previous year in case of Jan and Feb.

Rule 2: F2DV (First 2 digit value)

F2DV (First 2 digit value) is calculated based on the first two digit parts of year.  For instance, in case of 1985, F2DV is “1”.  When the first two digit part of year is multiple of 4, F2DV is zero.  Using these regularity, people can memorize these correspondence naturally.

Rule 3: MonthV (Month value)

It is required to memorize the correspondence in the table.

Pre-calculation to derive L2DV

This is the essence of 28/56/84 method.

It takes long time to calculate L2DV when the value of the last two digit value is large.  Therefore, we reduce this value using one of 28, 56, and 84.

28/56/84 method

Example 1: 2030/July/9

The first two digit is “20”, thus F2DV is “0” according to Rule 1.

L2DV pre-calculation is conducted, as the last two digit “30” is substracted by 28, that is “2”.  And the quotient of “2” is calculated (2 / 4 = 0  remainder 2).   Thus, the quotient is “0”.

MonthV is “5” based on Rule 3.

DayV is as is, “9”.

The sum of [1]F2DV(0), [2]pre-calculated value(2), [3]Quotient (0), [4]MonthV(5), [5]DayV(9) is 16(=0+2+0+5+9).  The remainder of the sum by 7 corresponds to the day of the week based on the table (16 /7 = 2  remainder 2), that is Tuesday.

Example 2: 1963/February/13

he first two digit is “19”, thus F2DV is “1” according to Rule 2.

Since the month is February, Rule 1 is applied.  We start L2DV calculation from “62”, which is previous year of “63”.  The last two digit “62” is substracted by 56, that is pre-calculated value “6”.  And the quotient of “6” is calculated (6 / 4 = 1  remainder 2).   Thus, the quotient is “1”.

DayV is as is, “13”.

The sum of [1]F2DV(1), [2]pre-calculated value(6), [3]Quotient (1), [4]MonthV(3), [5]DayV(13) is 24(=1+6+1+3+13).  The remainder of the sum by 7 corresponds to the day of the week based on the table (24 / 7 = 3 remainder 3).  Thus, that is Wednesday.

Other examples

Try!

Why don’t you try SpeedCalendar Timer to measure your calculation time.  It may takes one minute to calculate for the first time, but through several tryout, it will be less than 10 seconds.

If you wish to improve your time, see the thesis, which introduce “Kurukuru method”, “Full memorization method”.

How to calculate the day of the week

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