Day of the Week Calculator
Find the weekday, day of the year and ISO week number for any date.
Day of the week
Sunday
- Day of the year
- 201
- ISO week number
- 29
- Leap year
- No
Show the work
Days since Thursday, January 1, 1970
n = date − 1970-01-01
1969-07-20 − 1970-01-01 = −165
Count on from Thursday (4) and wrap every 7 days
weekday number = (4 + n) mod 7
(4 + (−165)) mod 7 = 0
Weekday number to name (0 = Sunday … 6 = Saturday)
0 = Sunday
How it works
Gregorian calendar; ISO 8601 weeks start on Monday and week 1 contains the first Thursday
Questions
- How does the day of the week calculator work?
- Gregorian calendar; ISO 8601 weeks start on Monday and week 1 contains the first Thursday.
- What do I need to enter?
- Date. Optional fields can be left blank.
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