📅 Calendar Calculator
Enter any date to find out what day of the week it falls on, along with its week number and day-of-year number.
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What this calculator does
The Calendar Calculator tells you the day of the week for any date, its position in the year as a day-of-year number, and its ISO week number.
How the calculation works
The calculator builds a real calendar date from the year, month, and day you enter and reads its weekday directly, which is exact for any date on the standard Gregorian calendar. The day-of-year count is the number of days since January 1st of that year, and the ISO week number follows the standard convention where week 1 is the week containing the year’s first Thursday.
This tool is for general scheduling, planning, and educational reference.
Last reviewed August 2026