The Day of the Week Calculator returns the weekday for any date in the Gregorian calendar, past or future, and shows the arithmetic behind the answer using Conway's Doomsday rule rather than only stating a result. Enter a date and the calculator names the weekday instantly, then walks through the same steps a person could use to work it out mentally, substituted with the entered date's own numbers.
Find the day of the week for any date
Every date in the Gregorian calendar maps to exactly one weekday, computed from the date's position relative to a fixed reference point rather than looked up in a table of finite size. The Day of the Week Calculator computes this directly for any date from 1583 onward, the year the Gregorian calendar took effect, and returns the weekday name immediately.
The same method works identically for a date decades in the past and a date centuries in the future, since the underlying arithmetic has no dependency on the current date or any stored range. Entering a birth date, a historical event, or a far-future scheduling date all use the same calculation.
Apply Conway's Doomsday rule
Conway's Doomsday rule finds a year's "doomsday," a single weekday that a specific set of easy-to-remember dates all fall on that year, then measures any other date in that year by its distance from the nearest one of those anchor dates.
The Day of the Week Calculator uses this method because it is fast enough to run by hand, which makes it worth showing rather than hiding behind a black-box result.
The rule runs in four steps for the year: find the century's anchor weekday from a lookup table, then compute three small values from the two-digit year and combine them with the anchor using arithmetic modulo 7. The result is the weekday that every doomsday date falls on that year, which becomes the reference point for finding any other date in the same year.
b = floor(twoDigitYear / 12)
c = twoDigitYear mod 12
d = floor(c / 4)
yearDoomsday = (centuryAnchor + b + c + d) mod 7Memorise the monthly doomsdays
A short list of dates falls on the year's doomsday weekday every single year, which is the memory trick that makes the rule practical without a calculator. The even months pair their number with itself: 4/4, 6/6, 8/8, 10/10, and 12/12 all fall on doomsday.
The odd months from May through November follow the mnemonic "I work from 9 to 5 at 7-11": 5/9, 9/5, 7/11, and 11/7.
March uses 3/14, the first three digits of pi. January and February are the exceptions, since they depend on whether the year is a leap year: 1/4 and 2/29 in a leap year, or 1/3 and 2/28 in a common year. Once one of these dates is known for the target year, any other date in that year is found by counting the number of days forward or backward from the nearest one and reducing that count modulo 7.
Find the day for 15 March 2292
Working out the weekday for 15 March 2292 by hand, using Conway's Doomsday rule, returns Tuesday. 1. Find the century anchor. The 2200s anchor to Friday, weekday index 5 in a table where Sunday is 0. **2.
Compute the year adjustment from 92, the two-digit year.** b = floor(92 / 12) = 7 c = 92 mod 12 = 8 d = floor(8 / 4) = 2
3. Combine with the anchor, modulo 7. 5 + 7 + 8 + 2 = 22, and 22 mod 7 = 1, which is Monday. 2292's doomsday weekday is Monday.
4. Find the nearest monthly doomsday to 15 March. March's doomsday date is 3/14, so 14 March 2292 is a Monday.
5. Step forward to the target date. 15 March is one day after 14 March, so it falls on Tuesday.
Read the ISO week number
The ISO 8601 week numbering system assigns every date a week number from 1 to 52 or 53, with every week beginning on Monday rather than Sunday.
Week 1 of a year is defined as the week containing that year's first Thursday, which means the first few days of January sometimes belong to the final week of the previous year instead of week 1 of the new one.
The Day of the Week Calculator reports the ISO week number alongside the weekday name for any date entered, which is the numbering system used in most of Europe for scheduling, payroll periods, and manufacturing date codes, distinct from the plain "week of the year" count some US contexts use starting from Sunday.
Name the day in ten languages
Weekday names translate directly across languages, and the Day of the Week Calculator returns the name of the calculated weekday in ten languages alongside the English result: Spanish, French, German, Italian, Portuguese, Japanese, Korean, Arabic, and Hindi, in addition to English itself.
Several of these languages preserve the same underlying naming pattern as English, since they descend from the same historical sources described below, while Japanese and Korean instead name weekdays after elements: sun, moon, fire, water, wood, metal, and earth, a completely separate naming tradition with no shared root.
Understand where weekday names come from
English weekday names come from two separate mythological traditions layered on top of each other. Sunday and Monday name the sun and the moon directly. Saturday preserves the Roman god Saturn without translation.
The remaining four days, Tuesday through Friday, were translated from Roman gods into their nearest equivalents in Norse mythology when Old English speakers adopted the seven-day week from Rome.
Tuesday comes from Tiw, a Norse god of war matched to Mars. Wednesday comes from Woden, matched to Mercury. Thursday comes from Thor, matched to Jupiter. Friday comes from Frigg, matched to Venus. Romance languages such as Spanish and French kept the original Roman planetary names more directly instead, which is why martes, mardi, and Mars all share an obvious root while Tuesday does not.
Frequently asked questions
What day of the week was a specific date?
Enter the date into the Day of the Week Calculator, and it returns the weekday directly, computed from the date's position in the Gregorian calendar rather than looked up from a limited table, so it works for any date from 1583 onward.
How does Conway's Doomsday rule work?
The rule finds a "doomsday" weekday for the target year using a century anchor and a short calculation from the two-digit year, then measures the target date's distance from the nearest easy-to-remember date that always falls on that doomsday weekday, such as 4/4 or 9/5.
What is the ISO week number?
The ISO 8601 week number runs from 1 to 52 or 53, with weeks starting on Monday and week 1 defined as the week containing the year's first Thursday. It is the standard week-numbering system used across most of Europe.
Why is Saturday named after a Roman god but Tuesday is not?
Saturday kept the Roman name Saturn directly. Tuesday through Friday were translated from their Roman planetary equivalents into the closest matching Norse gods when the seven-day week and its naming pattern reached Old English speakers, which is why Tuesday traces to Tiw rather than to Mars.
Can the calculator find the weekday for a date far in the future?
Yes. The calculation has no dependency on the current date, so it applies identically to a date centuries in the past or centuries in the future, within the Gregorian calendar's effective range starting in 1583.
What day of the week is a leap day, 29 February, on?
29 February is calculated the same way as any other date, using the doomsday date for February in a leap year, which is 2/29 itself. That means 29 February always falls on the same weekday as the year's doomsday.
Does the calculator show the day of the week in other languages?
Yes. Alongside the English weekday name, the calculator returns the equivalent name in Spanish, French, German, Italian, Portuguese, Japanese, Korean, Arabic, and Hindi.
Is the day of the week the same across all countries for a given date?
Yes. The Gregorian calendar and its weekday sequence are used internationally for civil purposes, so a given calendar date falls on the same day of the week everywhere, even though the local calendar date itself can differ by a day near midnight due to time zones.
Summary
The Day of the Week Calculator returns the weekday for any Gregorian calendar date and demonstrates the calculation using Conway's Doomsday rule, which finds a year's doomsday weekday from a century anchor and measures any date's distance from the nearest memorable anchor date.
Every result also includes the ISO week number, translations of the weekday name into nine other languages, and the historical origin of the English weekday names in Roman and Norse mythology.