Day of the week calculator

Find the weekday for a date, along with its day-of-year and ISO week.

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Updated 2026-09-20

Using Day of the week calculator

Choose a date to see its weekday. Calculations use the Gregorian calendar, independently of your device time zone. The ISO week-year can differ from the calendar year near New Year.

A worked example

January 1, 2000 was a Saturday. January 1, 2021 was a Friday in ISO week 53 of 2020.

Before you use the result

Years 0001–9999 use the same Gregorian rules. Historical local calendar reforms are not modelled, so this is not a historical Julian-calendar lookup.

Next: Calendar generator

Next: Week number calculator

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ToolOctopus. “Day of the week calculator.” Updated 2026-09-20. https://tooloctopus.com/day-of-the-week-calculator.

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