Day of the Week Calculator

Date & TimeLast updated: August 17, 2026

Knowing which day of the week a past or future date falls on is useful when you are planning a birthday or an anniversary, wondering about the day of a historical event, or putting together an event or holiday schedule. Because the calendar follows a cycle that only repeats every 400 years, working this out from memory is practically impossible.

Enter a date and you immediately see the day of the week (Monday through Sunday). You also get the day number and week number within the year, how many days are left until the end of the year, and whether that year is a leap year. You can query any date, from the 1900s through the 2100s.

Today's date is used by default; you can pick any date you are curious about.

Formula

Day of the week = derived from the calendar cycle (the modern equivalent of Zeller's rule)
Day of the year = the position of the date counted from January 1 (January 1 = 1)
Week of the year = Day of the year ÷ 7 (rounded up)
Leap year: the year is divisible by 4 and not by 100, or it is divisible by 400

The common mistake with leap years is to look only at divisibility by 4: 1900 is divisible by 4 but is not a leap year (it is divisible by 100 and not by 400), while 2000 is.

How to Calculate

  1. Pick the date you want to look up — it defaults to today.
  2. Read the day of the week at the top of the results section.
  3. Check the day and week number within the year and how many days are left until the end of the year.
  4. See whether the year is a leap year (365 or 366 days) in the last row.

Worked Examples

Calendar details for today

August 17, 2026 is a Monday. It is day 229 and week 33 of the year, with 136 days left until the end of the year. 2026 is not a leap year, so it runs 365 days.

Day of the week: Monday · Date: Monday, August 17, 2026 · Day of the year: Day 229

The first day of the millennium

January 1, 2000 was a Saturday — day 1 and week 1 of the year. Because 2000 is exactly divisible by 400, it is a leap year despite falling at the start of a century, and it ran 366 days; on that day, 365 days remained until the end of the year.

Day of the week: Saturday · Date: Saturday, January 1, 2000 · Day of the year: Day 1

The leap day: February 29

February 29, 2024 is a Thursday and is day 60, a date that only exists in leap years. Because 2024 is divisible by 4 and not by 100, it is a leap year of 366 days, with 306 days left until the end of the year.

Day of the week: Thursday · Date: Thursday, February 29, 2024 · Day of the year: Day 60

Frequently Asked Questions

How do I find out what day of the week I was born on?
Enter your date of birth in the date field and the calculator shows the day of the week straight away. Anyone born on January 1, 2000, for instance, was born on a Saturday. If you also want to know your exact age, use the age calculator.
How is a leap year determined?
A year is a leap year if it is exactly divisible by 4 and not divisible by 100; years divisible by 100 are leap years only if they are also divisible by 400. That is why 2024 and 2000 are leap years while 1900 and 2100 are not. In a leap year, February has 29 days and the year runs 366 days.
How is the week of the year calculated?
In this calculator the week number is found by dividing the day-of-year number by 7 and rounding up: January 1-7 is week 1, January 8-14 is week 2. It can differ by one week from the ISO 8601 week number, which is based on weeks starting on Monday.
Which date range is supported?
Any date in the modern (Gregorian) calendar can be looked up; the 1900s, 2000s, and later are safe to use. Because Turkey has used this calendar only since 1926, older Rumi or Hijri dates have to be converted to the Gregorian calendar first.
How often does the calendar repeat?
The Gregorian calendar has a full cycle of 400 years: August 17, 2026 and August 17, 2426 fall on the same weekday. Over shorter spans, the same date shifts to the next day of the week in the following year unless a leap year intervenes.
Where is the day-of-year number used?
The day-of-year number is used in agriculture, meteorology, and project period tracking; in some official and technical documents it appears under the name 'Julian day'. Day 229, for example, shows that roughly 63% of a 365-day year is already behind you.