Julian Date Converter
Convert between Gregorian calendar dates and Julian day numbers.
What is Julian Date?
Julian day numbers count continuous days since noon on January 1, 4713 BC. This tool converts between those numbers and calendar dates, including the Modified Julian Date (MJD).
How it works
It implements the standard Gregorian↔Julian day algorithms (the Fliegel–Van Flandern / Richards formulas), validating both directions for round-trip accuracy.
- Enter your input. Type or paste your input into the field above — the tool responds instantly.
- Review the result. Output updates live as you type. Everything runs entirely in your browser.
- Copy or download. Use the Copy button to grab the result, or Download to save it as a file.
Examples
Julian day number
Convert a Julian Day Number such as 2461268 to its Gregorian date — the continuous day count used in astronomy and some APIs.
Common mistakes
Julian day vs Julian calendar
A Julian Day Number is a continuous day count since 4713 BC — not the same as a date written in the Julian calendar, which is a different calendar system.
Frequently asked questions
What is a Julian Day Number?
The integer day count starting at noon on January 1, 4713 BC (Julian calendar) — used to avoid calendar complexities in calculations.
Does it handle fractional days?
Yes — decimal fractions convert to time-of-day, which matters for astronomical observations.
Can it convert today's date?
Yes — one click fills in today's Gregorian date and shows its Julian Day Number.