Day of the Week Calculator — what day was a date?

How it works

Every date falls on one of seven weekdays that repeat in a fixed cycle. To find which one, the calculator converts the date to a day number, then steps around the Monday-to-Sunday cycle from a known anchor — so you never have to count by hand.

Because the weekday depends only on the running count of days, it automatically respects different month lengths and leap years: a year is a leap year (with a February 29) if it is divisible by 4, except centurial years, which must be divisible by 400. That extra day shifts every following weekday by one, which the count handles for you.

The day of the year is simply how many days into the year the date falls: January 1 is day 1, and December 31 is day 365 in a common year or day 366 in a leap year.

Worked example

2026-08-06 is a Thursday — the 218th day of 2026. January 1, 2026 is also a Thursday and, of course, day 1. The leap day February 29, 2024 is the 60th day of that year (31 days in January plus 29 in February).

Frequently asked questions

What day of the week is a given date?

Enter the date and the calculator names the weekday. It converts the date to a day count and steps around the seven-day cycle from a fixed reference, so month lengths and leap years are handled automatically. For example, 2026-08-06 is a Thursday.

How is the day of the week calculated?

Each date has a running day number; dividing that number by seven and taking the remainder places it on the weekday cycle. Because the count includes every calendar day — including February 29 in leap years — the weekday is always exact without manual counting.

What is the day of the year?

It is the date's position within its year: January 1 is day 1, February 1 is day 32, and December 31 is day 365 (or 366 in a leap year). It is useful for deadlines, schedules and comparing progress through the year.

How do leap years affect the weekday?

A leap year adds February 29, which pushes every date after it one weekday later than it would otherwise fall. A year is a leap year if divisible by 4, except centurial years, which must be divisible by 400 — so 2000 was a leap year but 1900 was not.

Why does the same date fall on different weekdays in different years?

Because a common year has 365 days — 52 weeks plus one day — each date advances by one weekday the next year, or two after a leap year. That one- or two-day shift is why your birthday lands on a different day of the week each year.

Does the week start on Monday or Sunday?

Weekday names are the same either way; only the ordering convention differs. This calculator reports the weekday name itself (Monday, Tuesday, …), which is unambiguous. The day of the year is independent of where you consider the week to start.