Day of Week Calculator
Find the weekday for any valid date.
What day of the week was a given date?
Every calendar date falls on a fixed weekday, worked out from the proleptic Gregorian calendar.
Formula: The weekday is derived from the Gregorian calendar date; day of year counts elapsed calendar days from January 1.
What this calculator does
Find a date’s weekday, day of year, and leap-year status using the Gregorian calendar.
Use it to turn Date into a checked result you can compare, copy, or rerun with different assumptions.
The page shows the formula, a numeric worked example, and the assumptions that affect this everyday calculation.
Inputs and what they mean
- Date
- — date value.
How to use it
- Enter the dates, times, or schedule details.
- Adjust the available options for your situation.
- Review and copy the instant result.
Formula
The weekday is derived from the Gregorian calendar date; day of year counts elapsed calendar days from January 1.
Inputs used: Date.
Edge handling: Date is required.; Date must use a valid calendar date..
Worked example
Find a weekday
- Start with Date: 2026-09-14.
- Apply the method: The weekday is derived from the Gregorian calendar date; day of year counts elapsed calendar days from January 1.
- September 14, 2026 falls on a Monday.
Reading the result
The headline figure is the main answer. Any breakdown underneath shows the parts that make it up, so you can check the working and see what changes when you adjust an input.
Limitations and assumptions
- Inputs outside the supported range are rejected rather than forced into a result.
- The result depends on the values you enter for this day of week calculator; it does not supply missing rates, rules, prices, dates, or assumptions for you.
Common questions
What day of the week was a given date?
Every calendar date falls on a fixed weekday, worked out from the proleptic Gregorian calendar. Check the formula, example, and limitations on this page before using the result for a real everyday decision.
Are historical Gregorian dates supported?
The calculator uses the proleptic Gregorian calendar supported by JavaScript dates. Check the formula, example, and limitations on this page before using the result for a real everyday decision.
Does day of year handle leap years?
Yes. Dates after February include the leap day when applicable.
How do I use the Day of Week Calculator?
Enter the required values for Date. The calculator applies the formula on this page and shows the main result with any supporting breakdown so you can check the arithmetic.
What formula does the Day of Week Calculator use?
The weekday is derived from the Gregorian calendar date; day of year counts elapsed calendar days from January 1. The visible formula section above lists the calculation path and the edge cases the page handles, so the result can be checked without relying on the form alone.
Can the Day of Week Calculator be used for exact decisions?
Use it as a calculation aid, not as a substitute for checking the underlying rule, contract, policy, or professional advice that applies to your situation. When a result depends on local rules, personal details, prices, or dates, enter those values yourself and confirm them before acting.
Cite this page
Free Calculator. (n.d.). Day of Week Calculator. https://freecalculator.tech/tools/day-of-week-calculator
"Day of Week Calculator." Free Calculator, https://freecalculator.tech/tools/day-of-week-calculator.
Day of Week Calculator — Free Calculator, https://freecalculator.tech/tools/day-of-week-calculator
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