So, what day of the week does

Christmas day fall on?

- Select the year you are interested in. Break this into two parts: Century and Year.

example: 2001 becomes `C` = 20, and `Y` becomes 01.
- Divide
`C` by 4 and truncate. Store the result into `K`.

example: `K` = `C`/4 = 20/4 = 5
- Divide
`Y` by 4 and truncate. Store the result into G.

example: `G` = `Y`/4 = 1/4 = 0
- D = 50 +
`Y` + `K` + `G` - (2 * `C`)

example: 50 + 1 + 5 + 0 – 40 = 16
- Take the remainder of D/7 (or take the modulo: D % 7)
example: 16 % 7 = 2
- Lookup:

Please note that this applies only to the

Gregorian calendar that was first introduced in 1582.