Enter any date and find out exactly which day of the week it falls on. Just pick a date using the date picker and the calculator returns the day name, along with the day of the year, week number, and how many days until or since that date from today.
Day of the Week
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Full Date
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Day of the Year
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ISO Week Number
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Days From Today
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Weekend or Weekday
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The calculator uses JavaScript's built-in Date object to parse the date you enter and determine the corresponding weekday. It applies the same algorithm used by the internationally recognized ISO 8601 standard, which defines Monday as the first day of the week. The result is displayed immediately as a named day (e.g., Monday, Friday).
Yes — the calculator works for any date, whether it's in the past or far in the future. Simply select a future date using the date picker and the day name will be shown instantly.
The ISO week number is defined by ISO 8601 and counts weeks starting on Monday. Week 1 of the year is the week that contains the year's first Thursday. Most years have 52 weeks, but some years have 53.
The days of the week in English are named after celestial bodies and Norse/Roman gods. For example, Sunday is named after the Sun, Monday after the Moon, Tuesday after Tiw (Norse god of war), Wednesday after Woden, Thursday after Thor, Friday after Frigg, and Saturday after Saturn.
The calculator is fully accurate for all dates within the Gregorian calendar, which has been the internationally adopted standard since October 15, 1582. For dates before that, results reflect the proleptic Gregorian calendar.
No installation is needed. The calculator runs entirely in your browser using JavaScript, so you can use it on any device — desktop, tablet, or mobile — without downloading anything.
Zeller's congruence is a mathematical algorithm invented by Christian Zeller in the 19th century for calculating the day of the week for any date in the Julian or Gregorian calendar. Modern calculators like this one achieve the same result using built-in date functions in programming languages.
The 'Days From Today' field shows how many days separate the date you entered from today's date. A positive number means the date is in the future; a negative number means it is in the past.