Weekday & calendars

Choose a Gregorian date from 1583 to 9999. Results update immediately. Today restores the current local date; small date drafts survive navigation and reload. An empty or invalid date removes the old results.

The weekday, day of year and ISO week use the selected civil date independently of your time zone. ISO weeks start on Monday; week 1 contains 4 January, so the week-year can differ from the calendar year. Gregorian and Julian dates are proleptic: historical local reforms are not modelled.

JDN is the integer Julian day number associated with noon on that date. The Julian date at midnight is JDN − 0.5. For 1 January 2000, JDN is 2451545; it is not a date in the Julian calendar.

Other calendars use your browser’s Intl/ICU data at 00:00 UTC. Unsupported calendars are marked unavailable rather than silently replaced. Names, month forms and distant-date extrapolations can vary between browsers. Islamic dates do not predict local moon sightings; religious days starting at sunset and historical era boundaries are not simulated. These rows compare calendar representations, not official observances.