Formula
Weekday = day name of the entered calendar date evaluated at UTC midnight in the proleptic Gregorian calendar.
Time & Date
Day of the Week Calculator
Find the weekday for any calendar date using year, month and day inputs.
Calculator
Working calculator
Live resultFriday2026-05-15 at UTC midnight · Gregorian calendar weekday
Formula used
Weekday = day name of the entered calendar date evaluated at UTC midnight in the proleptic Gregorian calendar.
This is the method behind the answer, so the result can be checked rather than simply trusted.What-if check
Nearby dates
Weekdays move one step at a time and repeat every seven days. The rows below make the cycle visible around the selected date.
| Offset | Date | Weekday |
|---|---|---|
| -7 days | 2026-05-08 | Friday |
| -1 days | 2026-05-14 | Thursday |
| Selected date | 2026-05-15 | Friday |
| +1 days | 2026-05-16 | Saturday |
| +7 days | 2026-05-22 | Friday |
Visual proof
Seven-day cycle
The gold marker shows where the selected date lands in the repeating seven-day weekday cycle.
Printable calculation report
Result: Friday. Assumption: Inputs use the modern Gregorian calendar convention used for ordinary civil dates.
- Year
- 2026
- Month
- 5
- Day
- 15
- Page/date context
- 2026-05-16 UTC page version
- Page URL
- https://calculationtime.com/calculators/day-of-week-calculator
Worked example
For 15 May 2026, the calculator creates the UTC date 2026-05-15. The calendar weekday for that date is Friday, so the result is Friday.
Professional note
Master’s Tip: for birthdays, schedules and school planning, the Gregorian weekday is usually enough. For historical records before local Gregorian adoption, check the calendar system used in that place and year before quoting the weekday.
Regional and unit assumptions
The basis is transparent general calendar arithmetic using numeric year-month-day inputs and UTC midnight. No legal deadline, holiday or regional adoption rule is claimed.
Assumptions and limitations
- Inputs use the modern Gregorian calendar convention used for ordinary civil dates.
- The calculation evaluates the date at UTC midnight to avoid daylight-saving hour shifts.
- Very old historical dates may have used Julian or local calendar rules rather than the Gregorian calendar.
- Invalid month/day combinations can normalise in JavaScript Date arithmetic, so confirm unusual dates such as 31 April before relying on them.
Methodology & Accuracy
How this calculator is checked
CalculationTime pages are built around visible arithmetic: the formula, assumptions, worked example and practical limitations are shown so the result can be checked rather than simply trusted.
Formula used
Weekday = day name of the entered calendar date evaluated at UTC midnight in the proleptic Gregorian calendar.
Standard or basis
The basis is transparent general calendar arithmetic using numeric year-month-day inputs and UTC midnight. No legal deadline, holiday or regional adoption rule is claimed.
Where a calculator follows a named legal, trade or industry standard, that standard is cited visibly. Otherwise the page uses transparent general arithmetic and states its limits.Master's Tip
Master’s Tip: for birthdays, schedules and school planning, the Gregorian weekday is usually enough. For historical records before local Gregorian adoption, check the calendar system used in that place and year before quoting the weekday.
Related calculators
Questions
How do you find the day of the week for a date?
Create the calendar date from the year, month and day, then read the weekday assigned to that date in the Gregorian calendar.
Why use UTC midnight for the weekday?
UTC midnight keeps the calculation date-only, so daylight-saving time changes do not shift the result by an hour.
Can this be used for very old historical dates?
Use caution. Many places used Julian or local calendars before adopting the Gregorian calendar, so historical weekdays may depend on the calendar system in use.
Does this include holidays?
No. It only returns the weekday name. Holidays, observances and business-day rules are separate calendar layers.
Calculation note
Weekday calculation connects ordinary scheduling with calendar history. A day name looks simple, but it depends on a shared calendar system, the seven-day week and the convention used to map numbered dates onto weekdays.
The seven-day week is a repeating cycle
Weekday calculation works because weekday names repeat in a fixed seven-day cycle. Once a calendar date is mapped onto that cycle, moving forward or backward by seven days lands on the same weekday.
The Gregorian calendar matters for modern dates
Modern civil dates usually use the Gregorian calendar. Leap-year rules keep the calendar aligned with the solar year, which is why weekday arithmetic must account for month lengths and leap days rather than simply counting every year as 365 days.
Historical dates need calendar context
Different countries adopted the Gregorian calendar at different times. A printed historical date can therefore have a different weekday depending on whether the Julian calendar, Gregorian calendar or a local convention was used.
Sources and further readingBritannica: Gregorian calendarNIST: Time and frequency from A to Z