Julian Day Number Converter
Convert between a Gregorian calendar date, its Julian Day Number (the continuous day count used in astronomy and chronology, where the Julian period starts 1 January 4713 BC), and a Unix timestamp. The Julian Day Number is the standard for date arithmetic that works across any calendar and avoids month/year boundaries. Also shows the day of the week and the day of the year. Runs locally in your browser.
Inputs (edit any one)
Result
The Julian Day Number (JDN) counts days from 1 January 4713 BC (Julian), starting at noon. Here we use the integer JDN for the whole Gregorian day: 2000-01-01 = 2451545 (the J2000.0 epoch), 1970-01-01 = 2440588 (the Unix epoch). Edit the date, the JDN, or the Unix timestamp and the others update. The Unix timestamp is derived as (JDN − 2440588) × 86400 (so JDN↔day, with the time-of-day at midnight UTC); a Unix timestamp converts to the JDN of its day with floor(ts / 86400) + 2440588. The day of the week follows from JDN mod 7 (JDN 0 = Monday). This is the proleptic Gregorian calendar (Gregorian rules projected backward). Pairs with the Timestamp Converter, Day-of-Year, and Date Duration tools. Everything runs locally — nothing leaves your browser.