What Day of the Week?
Find the day of the week for any date — the day you were born, a wedding or historical date, or a date far in the future. See the same date across the surrounding years, and follow the step-by-step working. It runs entirely in your browser.
Today is a
Sunday
Today, September 13, 2026, is a Sunday.
Weekend or weekday
Weekend
Day of the year
256 of 365
Leap year
No
Share
Show the working (Doomsday method)
Conway's Doomsday algorithm reaches any date from a weekday that a handful of easy dates share each year. Here is how it lands on September 13, 2026:
- The anchor day for the 2000s is Tuesday.
- Applying the year's offset gives the doomsday for 2026: Saturday.
- A doomsday in September is the 5th, which is that same weekday.
- The 13th is8 days later, shifting the weekday to Sunday.
The Same Date Across the Years
What weekday September 13 falls on in nearby years. Weekends are highlighted — handy for spotting when a birthday or anniversary next lands on a Saturday or Sunday.
| Year | Weekday | Type |
|---|---|---|
| 2023 | Wednesday | Weekday |
| 2024 | Friday | Weekday |
| 2025 | Saturday | Weekend |
| 2026 (selected) | Sunday | Weekend |
| 2027 | Monday | Weekday |
| 2028 | Wednesday | Weekday |
| 2029 | Thursday | Weekday |
| 2030 | Friday | Weekday |
| 2031 | Saturday | Weekend |
| 2032 | Monday | Weekday |
| 2033 | Tuesday | Weekday |
| 2034 | Wednesday | Weekday |
| 2035 | Thursday | Weekday |
| 2036 | Saturday | Weekend |
How a Date Maps to a Weekday
The seven-day week runs unbroken across the entire Gregorian calendar, so every date has exactly one weekday, the same for everyone regardless of location. A common year is 365 days — 52 weeks and one day left over — so a fixed date usually slides forward one weekday each year. After a leap day it slides forward two, which is why any date eventually visits all seven weekdays.
Because the leap-year rule repeats every 400 years, so does the whole weekday pattern: the Gregorian calendar is identical every four centuries. Within the 1901–2099 window (which has no skipped century leap year) the shorter 28-year cycle holds, so your birthday falls on the same weekday every 28 years.
This tool computes the weekday from the Julian Day Number — a running day count used in astronomy — so a single uniform rule covers every date, whether it is centuries in the past or far in the future.
Frequently Asked Questions
Every calendar date maps to a fixed weekday, so the answer never depends on time zone or the current moment. This tool converts the date to a Julian Day Number — a continuous count of days used in astronomy — and takes that number modulo 7. Because it works from the day count, one uniform rule covers every date, from the distant past to the far future, with no special cases. The "Show the working" panel demonstrates the same result using Conway's Doomsday method, the mental-math technique many people use to do this in their head.
Enter your date of birth above and the weekday appears instantly, along with the same birthday across the surrounding years so you can see when it next falls on a weekend. The calculation itself runs in your browser. The "Copy link" button places the chosen date in the page address so you can share a pre-filled result — the date travels only as part of that address, and only if you choose to share it.
Yes, with one caveat. The calculation uses the proleptic Gregorian calendar — the modern leap-year rules projected backward — for every date. Most countries did not adopt the Gregorian calendar until 1582 or later (Britain and its colonies in 1752), so for dates before adoption the weekday shown is the proleptic-Gregorian one, which can differ from the Julian-calendar weekday recorded at the time. For any date from the late 1500s onward in Gregorian-using regions, the result matches the historical record.
A common year is 365 days, which is 52 weeks plus one extra day, so a fixed date normally advances by one weekday each year. A leap year adds a second day, so after a February 29 the date jumps forward by two weekdays. That is why a given date cycles through all seven weekdays, and why the full pattern repeats only every 28 years (in the 1901–2099 stretch with no skipped leap years).
In Conway's Doomsday algorithm, a "doomsday" is a set of easy-to-remember dates — 4/4, 6/6, 8/8, 10/10, 12/12, plus a few odd-month anchors — that all fall on the same weekday within any given year. Once you know that weekday (the year's "doomsday"), you can reach any nearby date by counting days forward or backward. The working panel shows the anchor it used and the offset it counted for your date.