Weekday Calculator — What Day of the Week Is Any Date?
Enter any year, month and day to find the exact day of the week — Sunday through Saturday — and instantly see whether it falls on a weekday or the weekend.
How does this calculator work?
Enter any year, month and day to get the weekday name. Internally, the calculator uses the JavaScript Date object's getDay() method — which applies the proleptic Gregorian calendar — returning 0 for Sunday through 6 for Saturday. Invalid dates like February 30 are detected and rejected rather than silently rolling over.
Formula
How this is calculated
The calculation constructs a Gregorian calendar date from the entered year, month and day using the platform's built-in Date object and reads the day-of-week index with getDay() — 0 for Sunday, 1 for Monday, … 6 for Saturday. This approach is correct for all years the Gregorian calendar is valid (1583 onward for the proleptic Gregorian calendar; JavaScript extends it to year 1 for convenience).
The calculator also validates the date itself: invalid calendar dates such as February 30 or April 31 are rejected rather than silently rolling over (e.g. February 30 would become March 1 in JavaScript, giving the wrong day for the intended date). If the date rolls over, a warning is shown instead.
A secondary readout shows the numeric day index (0–6), a weekday/weekend label, and a timeline bar visualising the day's position in the Sunday-to-Saturday week. This makes it easy to see at a glance how far through the week the date falls.
Frequently asked questions
The calculator uses the JavaScript Date object, which internally implements a variant of the Julian Day Number (JDN) algorithm to convert any proleptic Gregorian date to a weekday. It is accurate for any year from 1 to 9999 within the proleptic Gregorian calendar.
February has at most 29 days (in a leap year) and at most 28 in other years. If you enter an impossible day for a given month, the JavaScript Date object silently rolls the date over to the next month (e.g. Feb 30 becomes Mar 1 or 2). The calculator detects this rollover and rejects it to avoid returning the wrong weekday for a date you never intended.
A Gregorian year is a leap year if it is divisible by 4, except for century years (divisible by 100), unless also divisible by 400. So 2000 and 2400 are leap years, but 1900 and 2100 are not. The Date object handles this correctly for all years in the valid range.
Also known as
TG we-Calculate Editorial Team. (2026). Weekday Calculator — What Day of the Week Is Any Date? [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/weekday-calculator
TG we-Calculate Editorial Team. "Weekday Calculator — What Day of the Week Is Any Date?." TG we-Calculate. 2026. https://we-calculate.com/calculator/weekday-calculator.
TG we-Calculate Editorial Team, "Weekday Calculator — What Day of the Week Is Any Date?," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/weekday-calculator
@misc{wecalculate_weekday_calculator, title = {Weekday Calculator — What Day of the Week Is Any Date?}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/weekday-calculator}}, year = {2026}, note = {TG we-Calculate} }
Did this calculator help you?