Convert any calendar date to its Modified Julian Date (MJD) — or go the other way and turn an MJD number back into a standard Gregorian calendar date. Enter a date and optional UTC time to get the precise MJD value, or enter an MJD number to retrieve the corresponding calendar date, day of week, and Julian Date.
Result
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Calendar Date
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Julian Date (JD)
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Day of Week
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Unix Timestamp (seconds)
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Modified Julian Date is a compact time-tracking system derived from the Julian Date. It starts at midnight on November 17, 1858 (MJD 0), rather than the Julian Date's noon epoch in 4713 BC. MJD = JD − 2400000.5, making it a smaller, more convenient number for modern computing, astronomy, and geodesy.
The Julian Date counts days continuously from noon on January 1, 4713 BC, resulting in large numbers (currently around 2.46 million). MJD subtracts 2,400,000.5 from the JD, resetting the epoch to midnight on November 17, 1858. This cuts the number down significantly and aligns the day boundary with midnight instead of noon.
MJD is widely used by astronomers, satellite operators, geodesists, and space agencies including NASA and the US Naval Observatory. It was originally introduced by the Smithsonian Astrophysical Observatory to track the Sputnik satellite orbit using only 18 binary digits.
MJD 0 corresponds to midnight at the start of November 17, 1858, in the Gregorian calendar. This is equivalent to Julian Date 2400000.5.
Select 'Calendar Date → MJD', enter your date and optionally a UTC time, then read the MJD result. The formula accounts for the Gregorian calendar structure: MJD = JD − 2400000.5, where JD is computed from the year, month, day, and fractional time of day.
Switch the direction to 'MJD → Calendar Date' and enter the MJD number. The calculator computes the corresponding Julian Date (JD = MJD + 2400000.5) and then reverse-converts it to a Gregorian year, month, and day, along with the day of the week.
MJD increases by exactly 1.0 per day. As of early 2025, the MJD is approximately 60690–60750. Use this converter with today's date to get the precise current MJD including any fractional day from your UTC time input.
Yes. MJD is a real number, not just an integer. The fractional part represents the fraction of the day elapsed since midnight UTC. For example, MJD 60690.5 represents noon UTC on that day. This converter supports fractional MJD when you provide a UTC time.