What day of the week is this date?

Pick any date — a birthday in 1998, a deadline in 2027, the day you were born — and get its weekday, its ISO week number, and where it sits inside its year.

Example

Friday, 25 December 2026 is day 359 of 2026, falls in ISO week 52 of 2026, and 2026 is not a leap year — so its February had 28 days. Every figure under the picker above is computed the same way for whatever date you enter.

What is an ISO week number?

The ISO 8601 week system is the one used on most European calendars and in much of business planning. Weeks start on Monday, and week 1 of a year is the week containing that year's first Thursday. A side effect worth knowing: the last days of December can belong to week 1 of the next ISO year, and the first days of January can belong to the last week of the previous one — which is why this page shows the ISO week-year alongside the week number when they differ from the calendar year.

Questions, answered

How is the weekday calculated?

By counting whole days from a known reference date on the UTC calendar. No time-of-day and no time zone enters the math, so the answer is the same everywhere on Earth — a date has one weekday, unlike a moment in time.

What weekday was I born on?

Enter your birth date above. Dates before 1970 and after 2038 work fine here; the math is pure calendar arithmetic, not tied to a 32-bit clock.