Tools
Numbers & Dates
Day of Week
What day of the week does any date fall on? Works for any date in history or the future.
Works for any date — past, present, or future.
How it works
The idea
Every date maps to a number 0–6 (Sun–Sat). The calculator uses modular arithmetic — dividing by 7 and taking the remainder — to find which day a date falls on.
Month offset table
Each month starts a set number of days offset from Jan 1.
Jan0
Feb3
Mar3
Apr6
May1
Jun4
Jul6
Aug2
Sep5
Oct0
Nov3
Dec5
Example
July 20, 1969 (Moon landing)
Month code for Jul = 6
Day = 20
Year math: 69 + ⌊69/4⌋ = 69 + 17 = 86
Century offset for 1900s = 0
(6 + 20 + 86 + 0) mod 7 = 112 mod 7 = 0
0 = Sunday ✓