Day of the Week Calculator
Find the weekday for any date and its day number within the year.
Find out what day of the week any date falls on — past, present, or future — along with its position in the calendar year.
How Day of the Week Calculator Works
The calculator reads your selected date directly using standard calendar logic, which inherently accounts for varying month lengths and leap years, then returns the weekday name that date falls on.
It also calculates the date's "day of year" (its position counting from January 1st as day 1) and its ISO weekday number, where Monday is counted as day 1 and Sunday as day 7 — the international standard used in many scheduling and business systems, as opposed to the common US convention of starting the week on Sunday.
See It In Action
Who Uses Day of the Week Calculator and Why
- Finding out what day of the week a specific past date fell on, like a birthday or historical event.
- Checking what weekday a future date lands on before scheduling something, such as confirming a deadline doesn't fall on a weekend.
- Getting a date's day number within its year for scheduling or manufacturing systems that use numbered day codes.
- Satisfying curiosity about which weekday a date far in the past or future falls on.
Mistakes to Avoid
- Assuming the calculation applies uniformly to dates before a country's adoption of the Gregorian calendar — very old historical dates may have followed a different calendar system.
- Confusing the day-of-year number with the day-of-week — this tool reports both, but they answer different questions (Tuesday vs. day 214, for example).
Tips for Best Results
- Use the day-of-year figure if you need to cross-reference a date against a system that tracks dates as a numbered count (common in manufacturing date codes and some billing cycles).
- This is a quick way to confirm a planned date doesn't accidentally fall on a weekend before locking in a deadline.
Fixing Common Problems
The weekday looks wrong for a very old historical date. — The standard Gregorian calendar math applies consistently going forward, but be aware that dates before a given country adopted the Gregorian calendar historically followed a different system, which this calculator doesn't account for.
Terms Explained
Day number: A date's position within its own calendar year, counted from 1 on January 1st up to 365 or 366.