Day of the Week Calculator
Enter any date to instantly find the day of the week, day number of the year and ISO week number.
How to Use the Day of the Week Calculator
Enter any valid calendar date to find the weekday on which it falls.
Practical Example
Entering 1 January 2026 returns Thursday.
Factors That Affect the Result
The calculation depends on the calendar date supplied. Historical calendar changes and local conventions may matter for very old dates.
Frequently Asked Questions
Does leap year matter?
Yes. Leap years affect weekday progression after February.
Can I enter future dates?
Yes.
Does time zone matter?
Not for a plain calendar date without a time.
Related Tools
How the Day of the Week Is Determined
A calendar date can be mapped to one of seven weekdays using the rules of the selected calendar. This is useful for checking historical dates, planning future events, verifying deadlines, or finding the weekday of a birthday or anniversary without manually paging through a calendar.
Dates and Calendar Rules
Leap years affect the weekday sequence after February because they add an extra day. Modern date tools generally use the Gregorian calendar for contemporary dates. Very old historical dates can be more complicated because countries adopted the Gregorian calendar at different times. For ordinary planning, enter the complete date and use the returned weekday directly. Remember that the weekday itself is independent of time zone when you are working with a calendar date rather than an exact timestamp near midnight.