What Day of the Week Was It?
Enter any date — past or future — and instantly get its weekday, plus its day-of-year and ISO week number.
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Weekdays, day-of-year and ISO weeks
Every date maps to a weekday through the Gregorian calendar's 400-year cycle, and this calculator reads it directly — no lookup tables needed. You also get the day-of-year number (Feb 1 is day 32) and the ISO 8601 week number used on European planners and in logistics. The table shows which weekday the same date hits for the next five years, so you can spot the next year your birthday lands on a Saturday.