Julian / Gregorian dates
Convert the same civil day between explicitly selected Julian and Gregorian calendars.
Your inputs
Choose your dates and the calculation convention. Results update as you edit.
Calculations run in your browser. Inputs are not saved or sent to analytics.
How it works
- → Julian day number → Resulting date
- Worked example: The Gregorian date 2000-01-01 corresponds to 1999-12-19 in the Julian calendar. This 13-day difference is specific to that period; it is not a fixed offset for every century.
- Gregorian calendar: 2000-01-01 ↔ Julian calendar: 1999-12-19.
Input and formula key
Your result
Complete the inputs to see your result.
Assumptions and limitations
Both calendars are extended mathematically over years 1–9999. The selected calendar is explicit; no country’s historical adoption date is inferred.
Sources
- US Naval Observatory — Calendars and conversion algorithms Sources reviewed: 2026-10-05
- US Naval Observatory — Calendar leap rules and historical adoption Sources reviewed: 2026-10-05
