Day of the Week Calculator
Find out what day of the week any date falls on, for past or future dates.
Results update as you type.
About this calculator
A day of the week calculator tells you which day a given date lands on — Monday through Sunday — for any date, past or future, using the browser’s proleptic Gregorian calendar. Alongside the weekday it reports the day number within the year (1–365 or 366), the ISO-8601 week number, whether the year is a leap year, and how many days remain until the end of the year. It is handy for planning events, checking historical dates, or working out which weekday a birthday or anniversary falls on in a future year.
You simply enter a date (or leave it blank for today) and it maps that date to a definite weekday using the proleptic Gregorian calendar built into every browser — the modern calendar rules projected consistently backward and forward in time. The same lookup yields the day-of-year number, the ISO week the date belongs to, and whether that year carries a 29 February, so a single answer covers several common questions at once.
For example, 4 July 1776 was a Thursday, and 1 January 2000 was a Saturday; enter your own birthdate and you can see which weekday you were born on, then check which weekday it falls on this year. People use it to plan events onto a particular weekday, settle "what day was I born" questions, verify a historical date, or work out that a fixed-date holiday shifts to a new weekday each year.
Frequently asked questions
How is the day of the week determined?
The calculator uses the proleptic Gregorian calendar (the same one built into every browser), which projects today’s calendar rules backward and forward, so any date maps to a definite weekday from Monday to Sunday.
What is the ISO week number?
Under ISO 8601, weeks start on Monday and week 1 is the week containing the first Thursday of the year (equivalently, the week with 4 January). That means early-January or late-December dates can belong to week 52/53 of the neighbouring year.
Does it work for dates before 1900 or far in the future?
Yes. Because it uses the proleptic Gregorian calendar it handles historical and future dates consistently, though for very old real-world dates the historical calendar in use at the time (e.g. Julian) may have differed.
What day of the week was I born?
Enter your date of birth and the calculator names the weekday it fell on, plus the day-of-year number and whether it was a leap year — a quick way to settle "what day was I born".
Why does a birthday fall on a different weekday each year?
A common year is 365 days, which is 52 weeks plus one extra day, so a fixed date usually advances one weekday each year and two across a leap year. Enter the date for different years to see the pattern.
Leave the date blank — what happens?
If you leave the field empty the calculator uses today’s date, so it doubles as a "what day is it today" check along with the day-of-year and week number.
Does it tell me if the year is a leap year?
Yes. It reports whether the date’s year is a leap year (366 days) or a common year (365 days), which also explains why the day-of-year total can reach 366.
Results are estimates for general guidance only, not financial, medical or tax advice.