Day of the Week Calculator
Pick any date. You get the weekday, which day of the year it is, its ISO week number, whether the year is a leap year and how many days are left in the year.
Your numbers
How we calculate it
The calendar date is turned into a count of days in UTC on the Gregorian calendar, and the weekday follows from that count, so a time zone can never change the answer. The day of the year is the number of days since 1 January, counting 1 January as day 1.
The ISO week starts on Monday, and week 1 is the week that contains the first Thursday of the year. For 15 March 2026 the calculator gives Sunday, day 74 of the year, week 11 of 2026, a year that is not a leap year, and 291 days left.
Assumptions and limits
- Dates use the Gregorian calendar throughout, even before it was adopted in 1582. For old dates this is the modern way of counting and not the calendar people used at the time.
- Years from 1 to 9999 are supported.
- A date entered as 30 February or 31 April is rejected as not valid.
Frequently asked questions
How do I find the day of the week for any date?
Enter the date here. By hand you can use Zeller’s congruence or the doomsday method, which uses the fact that certain dates in every year fall on the same weekday.
What is an ISO week number?
It is the week number used in much of Europe and in business planning. Weeks run from Monday to Sunday, and week 1 is the week with the first Thursday of the year, so early January can be in the last week of the year before.
How do I tell if a year is a leap year?
A year is a leap year if it is divisible by 4, except for century years, which must be divisible by 400. So 2024 and 2000 are leap years and 1900 and 2100 are not.
Related calculators
- Week Number CalculatorPick a date to see which ISO week it falls in, the year that week belongs to, and the Monday and Sunday that start and end the week.
- Days Between Dates CalculatorPick two dates to see exactly how many days apart they are, along with the same gap in weeks, in years-months-days and in working weekdays.
- Add Days to a Date CalculatorStart with a date and add or subtract any number of days, weeks, months or years to find the resulting date.
- Age CalculatorEnter a date of birth to see your exact age and how many days until your next birthday.
Worked example (a fixed example using the starting numbers, it does not change as you type)
Inputs: Date = March 15, 2026.
- Day of the week Sunday
- Day of the year 74
- ISO week Week 11 of 2026
- Leap year? No
- Days left in the year 291
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