Finding the day of the week for any date
The day of the week is the weekday name assigned to a complete calendar date: Monday, Tuesday, Wednesday, Thursday, Friday, Saturday or Sunday. To find it, you need the day, month and year. The same month and day can fall on different weekdays in different years.
A weekday calculation is useful when checking the day you were born, the weekday of a future birthday, or the calendar position of a past event. The date calculation here uses the Gregorian calendar.
How to calculate the day of the week
Weekdays repeat in a seven-day cycle. If one date is a Monday, the date seven days later is also a Monday. To find the weekday of another date, count the calendar days from a known reference date and use the remainder after division by seven to determine the weekday shift.
For example, January 1, 2001 was a Monday. January 2 was a Tuesday, and January 8 was again a Monday. Longer intervals follow the same cycle, but the count must include the actual lengths of months and any leap days.
A date-only weekday calculation does not need a birth time or event time. When converting a timestamp to a date, however, the time zone matters: the same moment can fall on different dates in different places.
Examples of days of the week
January 1, 2001: Monday. It was the first day of a common year with 365 days.
February 29, 2024: Thursday. This date existed because 2024 was a leap year.
October 4, 2026: Sunday. Under a Monday-to-Friday weekday convention, it is a weekend day.
To find your birth weekday, use the full date of birth. To find the weekday of your next birthday, use that birthday's upcoming year rather than the birth year.
How leap years shift weekdays
A common year has 365 days, equal to 52 weeks plus one day. A leap year has 366 days, equal to 52 weeks plus two days. This is why the weekday of a recurring date usually moves forward by one day, or by two when the interval crosses February 29.
Gregorian leap years are divisible by four, except century years must also be divisible by 400. The year 2000 was a leap year, while 1900 was not. February 29 is a valid date only in a leap year.
The shift depends on where the date falls relative to the leap day. Comparing the same date in consecutive years requires counting whether February 29 lies inside that specific interval.
ISO weekday numbers and week numbers
ISO weekday numbering starts with Monday as 1 and ends with Sunday as 7. The other values are Tuesday 2, Wednesday 3, Thursday 4, Friday 5 and Saturday 6. A numbering system that begins with Sunday will use different numbers for the same weekday names.
ISO calendar weeks also begin on Monday. Week 1 is the week containing January 4, which is also the week containing the year's first Thursday. An ISO week year may therefore differ from the calendar year near New Year's Day.
For example, January 1, 2021 was a Friday in ISO week 53 of 2020. January 4, 2021 was the Monday that began ISO week 1 of 2021.
Day of the year, remaining days and calendar quarter
The day of the year is an ordinal count beginning with January 1 as day 1. December 31 is day 365 in a common year and day 366 in a leap year. February 29, 2024 was day 60.
Remaining days are the dates after the selected date through December 31. Subtract the day-of-year number from the total days in that year. December 31 has zero remaining days, while January 1 has 364 or 365 remaining days.
Calendar quarters group months into four periods: Q1 is January–March, Q2 is April–June, Q3 is July–September and Q4 is October–December.
Weekdays for historical dates
A historical weekday depends on which calendar is being used. Countries adopted the Gregorian calendar at different times, and older records may use the Julian calendar or another system. Applying Gregorian rules to a historical date is not always the same as reproducing the calendar used locally at that time.
The dates here follow Gregorian rules throughout. When checking an old record, establish its calendar before comparing its weekday with a modern date calculation.
Frequently asked questions about days of the week
Why do I need the year to find a weekday?
The seven-day cycle continues across years. January 1 can be a different weekday in each year, so month and day alone do not identify a weekday.
Is Sunday the first or seventh day of the week?
It depends on the convention. ISO numbering places Monday first and Sunday seventh. Some calendar displays begin their week with Sunday.
Does a weekday mean a working day?
Not necessarily. Monday–Friday are labeled weekdays here, but holidays and local work schedules can make a weekday a non-working day.
Can I find the weekday of a future date?
Yes. Gregorian weekday rules apply to future dates as well as past ones. Include the intended year when selecting the date.
How can I find the days between two dates?
Use the Date Difference Calculator for the elapsed interval. A weekday identifies a date's position in the week rather than its distance from another date.
Why can an ISO week belong to another year?
ISO week years are organized around whole Monday-to-Sunday weeks. Dates near January 1 can belong to the last ISO week of the previous year, and dates near December 31 can belong to the first ISO week of the following year.