Time & Date · Calendar
Date Information Calculator
Look up everything about a date: the day of the week, ISO week number, day of the year, quarter, days left in the year, whether it's a leap year, the Julian Day Number, and the date in the Indian national, Islamic and Hebrew calendars.
How this is calculated
ISO week: the week (Monday–Sunday) containing the year's first Thursday is week 1 · JDN = Fliegel–Van Flandern formula
- Day of year
- 1 for 1 January … 365 or 366 for 31 December
- Julian Day Number
- Days since 1 January 4713 BC (Julian calendar) at noon — used in astronomy
Weeks are numbered by the ISO 8601 standard: weeks start on Monday and week 1 is the one containing the first Thursday of January — so 1 January can belong to the last week of the previous year. Other calendars are converted with your browser's built-in calendar data.
Assumptions & sources
- Gregorian calendar for all dates (proleptic before 1582).
- Other calendars come from your browser's ICU data; the Islamic calendar shown is the tabulated Umm al-Qura version, which can differ by a day from local moon sighting.
- 1ISO 8601 — Date and time format (week numbering, calendar dates) — International Organization for Standardization
- 2Calendrical Calculations (Reingold & Dershowitz) — Cambridge University Press
- 3A Machine Algorithm for Processing Calendar Dates (Fliegel & Van Flandern, 1968) — Communications of the ACM
Calculator ID TIME-DATEINFO-001 · version 1.0.0
Common questions
What week number is it?
The ISO week number, used in most of Europe and in business planning, starts weeks on Monday; week 1 is the week with the year's first Thursday. Some US systems number weeks differently.
Is the year a leap year?
A year is a leap year if it's divisible by 4, except century years, which must be divisible by 400 — so 2000 was a leap year and 1900 wasn't.