A day of the week calculator instantly tells you which weekday any date falls on. Whether it is your birthday, a wedding anniversary, the day a historical event happened, or a future appointment, you get the answer at a glance — no flipping through calendars.
This tool goes further than the weekday alone. It also shows the ISO 8601 week number, the day of the year (the count of days since January 1), whether the year is a leap year, how many days the date is from today, and the Western (tropical) zodiac sign often used for birthday horoscopes.
How to Use
1. Pick the date you want to look up.
2. The weekday appears in large type, with the ISO week number, day of year, ISO weekday number, and leap-year status shown below.
3. Click the 'Today' button to drop in the current date instantly.
4. You can enter any date, in the past or the future.
How It Works
The weekday is derived in the same way as classic formulas (such as Zeller's congruence) that map any Gregorian date to a weekday. Internally, the year, month, and day are converted to a running day count, and the remainder after dividing by 7 gives the weekday.
The ISO week number assigns each week to the year that owns its Thursday, and week 1 is the week containing January 4. Weeks start on Monday. The day of year counts from January 1 as day 1.
Reading the Results
The weekday is shown as one of Sunday through Saturday. The ISO weekday number runs Monday = 1 to Sunday = 7. An ISO week of 2024-W05 means the 5th week of ISO year 2024. Around the new year the ISO year can differ from the calendar year — for example, January 1, 2021 falls in week 53 of 2020 under ISO.
'N days from today' is the difference in days between the chosen date and today. The leap-year flag tells you whether that year's February has 29 days.
Frequently Asked Questions
How is the weekday calculated? ▾
The year, month, and day are converted internally into a running day count, and the remainder after dividing by 7 determines the weekday. This is the same principle as Zeller's congruence and gives an exact weekday for any date.
What is Zeller's congruence? ▾
It is a formula published by Christian Zeller in the 19th century that returns the weekday for a given year, month, and day. It treats January and February as months 13 and 14 of the previous year, and this calculator uses the same underlying principle.
What is a leap year? ▾
A leap year is a year whose February has 29 days. In the Gregorian calendar, years divisible by 4 are leap years, except years divisible by 100, which are not — unless they are also divisible by 400. So 2000 was a leap year, but 1900 was not.
Can I find out what day of the week I was born? ▾
Yes. Enter your date of birth and the tool shows the weekday you were born on. It also displays your Western zodiac sign, so you can see your birthday details together.
Is the weekday correct for very old historical dates? ▾
Dates before 1583 are computed with the proleptic Gregorian calendar. Because the Gregorian calendar was not introduced until 1582, the weekday may differ from the calendar actually in use then (such as the Julian calendar). For historical research, check the calendar used at the time.
This tool computes results using the proleptic Gregorian calendar. For dates before 1582, or where regional or calendar conventions differ, the weekday may not match the one actually observed at the time. For critical uses, verify against primary sources.