What Day Is It? Day of the Week Calculator
Date & TimeThe calculator opens on today's date, so the day of the week shows at once. Pick any date from 1753 on to get its weekday, the day before and after, the day of the year, the days left in the year and the ISO week.
Step by step
October 8, 2026 falls on a Thursday
- Count the days from January 1, 1970 (a Thursday) to October 8, 2026 and divide by 7. The remainder gives the weekday: a Thursday.
- The day before is a Wednesday and the day after is a Friday.
- October 8, 2026 is day 281 of the year, with 84 days left, in ISO week 41 of 2026.
Once every entry is valid, you’ll see each step of the calculation here.
Formula
- weekday
- 0 = Sunday, 1 = Monday, up to 6 = Saturday; January 1, 1970 was a Thursday, which is 4
- h
- Zeller's result: 0 = Saturday, 1 = Sunday, 2 = Monday, 3 = Tuesday, 4 = Wednesday, 5 = Thursday, 6 = Friday
- q
- day of the month
- m
- month counted from March = 3 to February = 14; January and February count as months 13 and 14 of the previous year
- K, J
- the last two digits of that year (K) and the century (J), so 2026 gives K = 26 and J = 20
How it works
The calculator turns the date into a running day number on the Gregorian calendar, the calendar used in the United States, and divides it by 7. Because January 1, 1970 was a Thursday, the remainder tells you which of the seven weekdays the date is. It is the arithmetic you do in your head when you say that 10 days after a Monday is a Thursday, only carried out across every year, month and leap day in between.
Open the page and the date field already holds today's date from your device, so what day is it today is answered before you touch anything. Change the date to find the weekday of a birthday, an anniversary, a deadline or an appointment. The day before and the day after are listed too, so "what day is tomorrow" is answered as soon as today is selected. The week number follows ISO 8601: weeks start on Monday and week 1 is the week with the first Thursday of the year, so January 1 can belong to week 52 or 53 of the previous year.
Many US calendars and payroll systems number weeks differently, starting on Sunday and counting the week with January 1 as week 1, so their week numbers can differ from the ISO number shown here: July 4, 2027 is week 28 on such a calendar but ISO week 26, and January 1 is always week 1 there while ISO can call it week 52 or 53. To count the days between two dates, use the days between dates calculator; to find your exact age or weekday of birth, see the age calculator.
The formula
The calculator uses the first line, which counts days. The second line is Zeller's congruence, a classic way to find a weekday by hand, and gives the same answer for every Gregorian date. For October 8, 2026: q = 8, m = 10, K = 26, J = 20, so h = (8 + 28 + 26 + 6 + 5 + 100) mod 7 = 173 mod 7 = 5, which is Thursday.
The tool starts at January 1, 1753. Great Britain and its American colonies moved from the Julian to the Gregorian calendar in September 1752 (September 2 was followed by September 14), so earlier dates in the colonies are recorded on a different calendar, and a weekday computed with Gregorian rules would not match old records. From 1753 on, every date follows the rules above.
Example
What day of the week is July 4, 2027?
- Count the days from January 1, 1970, a Thursday, to July 4, 2027 and divide by 7. The remainder puts the date on a Sunday. The date is day 185 of 2027, a common year of 365 days.
- The day before is a Saturday and the day after is a Monday. A federal holiday that falls on a Sunday is observed on the Monday after, so federal employees get Monday, July 5, 2027 off.
July 4, 2027 is a Sunday. The day before is a Saturday and the day after is a Monday.
Load this example into the calculatorFrequently asked questions
What day is it today and why is it important?
The calculator opens on the date from your device, so the day of the week for today shows without typing anything. Knowing the exact day matters for deadlines, bill due dates, appointments and schedules: many of them depend on whether a date lands on a weekday, a weekend or a holiday.
What is today's date?
The date field opens on today's date from your device, so the result shows today's month, day and year with its day of the week, for example October 8, 2026, a Thursday. It also gives the day of the year and the days left in the year. If the date looks wrong, check the date and time zone set on your device.
What day is tomorrow?
Tomorrow is the day after today. Leave today's date in the field and read the result "The day after". If today is a Thursday, tomorrow is a Friday, after Saturday comes Sunday and after Sunday comes Monday. Choose another date to see the day after that one.
How do I find the day of the week for any date?
Enter the date and read the weekday, or work it out by hand with Zeller's congruence shown under the calculator. A quicker mental method is to know one anchor date: July 4, 2027 is a Sunday, so July 11 and 18 are Sundays too, and the same date moves forward one weekday each common year and two after February 29.
Why did we switch to the Gregorian calendar?
The older Julian calendar added a leap day every 4 years without exception, so its year was about 11 minutes too long and the calendar drifted against the seasons by roughly 10 days by 1582. Pope Gregory XIII fixed that by skipping 10 days and dropping the leap day in century years not divisible by 400. Britain and its colonies, including those that became the United States, switched in September 1752.
What month and day is today on the 13-month calendar?
The 13-month International Fixed Calendar has 13 months of exactly 28 days, with an extra month, Sol, between June and July and one more day at the end of the year. It was proposed in the early 1900s and was never adopted as an official calendar, so this tool shows Gregorian dates only. The day of the year it prints is a good starting point if you want to convert a date yourself.
Which special days are celebrated in September?
In the United States, Labor Day falls on the first Monday in September and is a federal holiday. Patriot Day is September 11 and Constitution Day and Citizenship Day is September 17. Type any of these dates into the calculator to see which weekday it falls on in a given year.
What day of the week was I born?
Enter your date of birth in the date field. Any date from January 1, 1753 works, so you can also look up the weekday of a wedding, a graduation or a historic event. For your exact age in years, months and days, use the age calculator.
Why does the week number differ from my calendar?
This page uses the ISO 8601 week: Monday is the first day and week 1 contains the first Thursday of the year. Calendar apps that start the week on Sunday and call the week with January 1 week 1 often show a different number, and early January days can belong to week 52 or 53 of the old year.
- Federal Holidays (U.S. Office of Personnel Management)
- Gregorian calendar (Wikipedia)
- Zeller's congruence (Wikipedia)
- ISO week date (Wikipedia)