What does a day-of-week calculator do?
It maps a Gregorian calendar date to its weekday and provides supporting calendar details such as day-of-year, quarter and leap-year status.
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For optional supporting equipment or reference material, you can browse Undated calendars and planners (paid link) on Amazon.com. Record the dates and counting choices used in your calculation. Check local holidays, time zones and official deadlines independently. No purchase is required to use this calculator.
How does leap-year status affect the result?
Leap years contain February 29, which shifts the weekday alignment of later dates in that year.
What does day of year mean?
Day of year counts January 1 as day 1 and continues through 365 or 366 in a leap year.
Can historical calendar dates differ from this result?
This calculator applies the Gregorian calendar consistently. Very old local historical dates may have been recorded under other calendar systems before local adoption of the Gregorian calendar.
Worked example: Day of Week
Enter the following values in the Day of Week Calculator and calculate to reproduce this result. Dates below use year-month-day order.
- Calendar date: 2026-10-15
Example result: Thursday. October 15, 2026 falls on a Thursday.
Calculation used: Gregorian calendar weekday for 2026-10-15
How to interpret this example
The weekday follows the Gregorian calendar date entered. It is a calendar lookup, not a time-zone conversion. An event near midnight may fall on a different calendar date in another location, which must be resolved separately.
Frequently asked questions
Sources and methodology
This calculator uses transparent browser-side date/time arithmetic. The references below provide standards or official context relevant to the calculation.