Julian date converter

Convert between a Gregorian date, Julian date (JD) and modified Julian date (MJD).

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Updated 2026-09-20

Using Julian date converter

Julian dates count continuous days and fractions of a day. The integer changes at noon. Modified Julian dates subtract 2,400,000.5 and change at midnight. This tool calculates a UTC-based day count.

A worked example

January 1, 2000 at 12:00 UTC gives JD 2451545 and MJD 51544.5. Midnight that morning is JD 2451544.5.

Before you use the result

This is not the ordinal day code used on food packaging. It uses the Gregorian calendar even before 1582, accepts years 0001–9999, and does not convert to UT1 or terrestrial time. Decimal JD input rounds to milliseconds.

Next: Day of the year calculator

Next: Unix timestamp converter

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ToolOctopus. “Julian date converter.” Updated 2026-09-20. https://tooloctopus.com/julian-date-converter.

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