Day of the week calculator

How the weekday is found

Every date belongs to a fixed seven-day cycle, so the weekday depends only on how many days have passed since a known reference. The calculator uses the calendar built into your device, which already accounts for leap years and the Gregorian rules, then reports the weekday, the day of the year and the ISO week. The day of the year counts from 1 on 1 January: 24 October 2026 is day 297, because the nine months before October hold 273 days and 24 is added. In a leap year the running total gains a day from 29 February onward.

The ISO 8601 week number treats weeks as Monday to Sunday, and week 1 is the one containing the year's first Thursday. By that rule 24 October 2026 lies in week 43. A handy shortcut for the weekday itself is that the first of each month in a year follows a set pattern; the table lists it for 2026.

Reading past and future dates

The tool labels the date as today, a number of days in the past, or a number of days ahead, which is the quick check most people want when confirming a deadline or recalling an event. The weekend flag marks Saturday and Sunday, since the weekday alone is often what decides whether an office or a service is open. If you are reconciling the day of the year with another system, remember that the day-of-year count and the ISO week can belong to different years around New Year: the last days of December sometimes fall in week 1 of the following ISO year, and the first days of January can sit in the final week of the year before.