Free Tools

Day of the Week Calculator

Find out what day of the week any date fell on — or will fall on — in seconds. Pick a month, day, and year and click Calculate to see the day of the week, the week number, and how many days it is from today. It's free, requires no sign-up, and runs entirely in your browser. Use it for birthdays, anniversaries, historical dates, or planning something in the future.

Date to Check

Month

Day

Year

How to Find the Day of the Week for Any Date

1 Select the month and day from the dropdowns. Both default to today's date, so you can leave them as-is to check today.
2 Enter the year. Any year from 1 to 9999 works — a historical date, a birth year, or a year far in the future.
3 Click "Calculate." The day of the week appears instantly, along with the full date, day-of-year number, and ISO week number.
4 Try another date any time. Change the month, day, or year and click Calculate again — no page reload needed.

How the Calculation Works

The calculator counts days using today's calendar rules, applied consistently forwards and backwards in time. Here's what that means in practice:

📅

Proleptic Gregorian Calendar

The Gregorian calendar (the one used almost everywhere today) wasn't adopted until October 15, 1582, and different countries switched to it on different dates over the following centuries. To keep results simple and consistent, this tool projects today's Gregorian rules backward indefinitely — a method mathematicians call the "proleptic Gregorian calendar." That means dates before 1582 may not match what a local calendar of the time would have shown.

📅

Leap Years

A year is a leap year if it's divisible by 4 — except century years (divisible by 100), which are only leap years if they're also divisible by 400. So 2024 and 2028 are leap years, 1900 was not, but 2000 was. This rule keeps the calendar year (365.2425 days on average) aligned with Earth's orbit around the sun, and it directly affects which day of the week every date after February falls on.

📅

ISO 8601 Week Numbers

The week number shown uses the ISO-8601 standard: weeks start on Monday, and week 1 of a year is defined as the week containing that year's first Thursday. In practice, this means the first few days of January sometimes belong to the last week of the previous year, and the last few days of December sometimes belong to week 1 of the following year.

Frequently Asked Questions

Does this work for dates before 1582?

You can enter any year from 1 to 9999, but keep in mind the tool uses the proleptic Gregorian calendar — today's calendar rules projected backward in time. The Gregorian calendar wasn't adopted until October 15, 1582, and different countries switched at different times (some more than a century later), so the result for a pre-1582 date may not match what a local calendar of that era actually showed. The tool shows a note whenever this applies.

How is the ISO week number calculated?

It follows the ISO-8601 standard, not a simple "day ÷ 7." Weeks run Monday through Sunday, and week 1 of any year is whichever week contains that year's first Thursday. This is more reliable than counting from January 1st because it keeps every week a full seven days and consistent from year to year.

Why doesn't week 1 always start on January 1st?

Because January 1st doesn't always fall on a Monday. If January 1st is a Friday, Saturday, or Sunday, most of that week actually belongs to the previous year under ISO rules, so it's numbered as one of the last weeks of the prior year — and week 1 starts the following Monday. Likewise, the very end of December sometimes rolls into week 1 of the next year.

Does the calculator account for time zones?

No — and it doesn't need to. This tool only works with calendar dates (month, day, year), not specific moments in time, so there's no time-of-day or time zone to account for. Whatever date you enter is treated the same way no matter where you or your device happen to be.

Can I look up a date in the future?

Yes. Enter any future date and the calculator will tell you what day of the week it falls on, plus exactly how many days from today that is — handy for planning weddings, deadlines, trips, or checking whether a future birthday lands on a weekend.

What is the "day of the year" number used for?

It's the date's position within its calendar year — for example, March 14 is day 74 in a non-leap year. This number (sometimes called an "ordinal date") is commonly used in programming, manufacturing date codes, agriculture, and scheduling, where counting straight through the year is more convenient than working with month and day separately.

What determines whether a year is a leap year?

A year divisible by 4 is a leap year, unless it's also divisible by 100 — in which case it's only a leap year if it's divisible by 400 too. That's why 2024 and 2000 are leap years, but 1900 and 2100 are not. Leap years add a February 29th, which shifts the day of the week for every later date in that year by one extra day compared to a non-leap year.

Is this tool free, and is my data private?

Completely free, with no account or sign-up required. All of the math runs directly in your browser using JavaScript — the date you enter is never sent to a server. You can even disconnect from the internet after the page loads and the calculator will still work.