About this day of the week calculator
Knowing the weekday of a date answers everyday questions, such as which day a birthday falls on next year, and historical ones, such as what day of the week the Moon landing happened. This calculator works for any date from the year 1 to 9999 and also shows a calendar of that month, the ISO week number, the day of the year, how much of the year has passed, the zodiac sign, the season in both hemispheres, and the date in common formats. It explains where the name of each weekday comes from, which links the English names to the planets of the Roman week.
How to find the day of the week
- Choose a date. Pick a date in the Date box, or press a famous date such as Y2K.
- Press Find the day. The weekday appears first, with the origin of its name.
- Explore the details. Check the month calendar, the date facts, and the same date written in other formats.
Frequently asked questions
Which calendar is used for old dates?
The Gregorian calendar, extended back before its introduction in October 1582. Historians often give older dates in the Julian calendar, so a weekday for an early date may differ from what you read in a history book.
Why are the weekdays linked to planets?
The Romans named the seven days after the seven visible heavenly bodies: the Sun, the Moon, Mars, Mercury, Jupiter, Venus, and Saturn. English replaced several of them with Germanic gods, but the order stayed the same.
How is the week number calculated?
It follows ISO 8601: weeks start on Monday and week 1 is the week containing the first Thursday of the year. Early January days can therefore belong to the last week of the previous year.
How are the seasons decided?
They use meteorological seasons, which start on the first day of a month: spring is March to May in the Northern Hemisphere. The Southern Hemisphere has the opposite season.
Can I use dates before year 1000?
Yes. Type the year with four digits, such as 0800, in the date box. Any date from 1 January of year 1 to 31 December 9999 works.