Julian Date and MJD Converter

How to use Julian Date and MJD Converter

Gregorian day counting uses the numerical epoch JD2440587.5 at1970-01-01 midnight. Add the entered fraction of a nominal86400-second UT1 calendar day; MJD=JD−2400000.5. A JavaScript UTC date is only a calendar arithmetic container, not a UTC-to-UT1 conversion.

1. Enter ut1 gregorian date, ut1 clock, jd or mjd for reverse conversion.
2. Choose the stated convention and check the units and supported model.
3. Calculate, inspect the result, then copy or download it.

Good to know

• Gregorian1801–2099, UT1 only, no leap seconds or UTC/TT inference. Millisecond calendar output; double day-number precision limits finer accuracy. Full-precision day-number strings are retained for copy/download round trips.
• Runs locally. Text/JSON fields are capped at30,000 characters; stricter page-specific and numeric-string limits also apply. Numeric inputs are bounded to magnitude1e15 and nonzero magnitude at least1e-100 unless an exact-string mode states otherwise. Approximate summaries use12 significant digits; CSV numeric cells retain the complete stored value and potentially formula-like string cells gain a protective apostrophe; unsupported, non-finite or detected underflow states return an error.