Modified Julian Day to date converter

It uses only the number you supply: it does not consult the current clock, infer a timezone, contact a network service, or depend on a machine's locale. Integer MJD values identify UTC midnight, while a fractional part describes the time elapsed since that midnight. The result includes separate calendar fields plus stable date and timestamp strings for direct use in code, reports, and scientific data checks.

Enter the Modified Julian Day value you actually have

Provide the value in the mjd field as a finite decimal number. Modified Julian Day is related to the astronomical Julian Day by a fixed offset, but it has a particularly convenient civil-day boundary: an integer MJD begins at midnight UTC. For example, 51544.0 represents the start of January 1, 2000, while 51544.5 represents noon on that same date. Preserve any fractional digits from your source when the time matters. The converter accepts ordinary decimal notation and numeric scientific notation, then calculates solely from that value. It does not assume that an unlabeled number came from a local timezone, and it does not silently treat a Julian Day value as MJD. Check the label and scale in your source dataset before conversion, because confusing JD with MJD introduces an offset of millions of days rather than a small rounding discrepancy. The output repeats the accepted MJD so an automated pipeline can associate each response with its original observation. Missing, nonnumeric, infinite, and excessively large values are rejected explicitly instead of producing a plausible-looking date.

Understand the Gregorian date and UTC clock result

The response separates year, month, day, hour, minute, and second, and also supplies a date string and a complete timestamp ending in Z. That Z marks UTC; there is no local offset hidden in the calculation. The calendar is proleptic Gregorian, meaning Gregorian leap-year rules are extended backward even before the historical adoption of that calendar. This convention is deterministic and useful for computation, but a very old result may differ from the calendar label found in a historical archive that used the Julian calendar. Years use astronomical numbering, so year zero exists and corresponds to 1 BCE in historical notation. Fractional MJD values are converted to the nearest whole second. If rounding reaches the end of a day, the calculation advances to midnight of the following Gregorian day rather than returning an impossible 24:00:00 clock value. The structured fields are convenient for database columns, while the timestamp is suitable for logs and interchange. The response names both its calendar and time scale so downstream code does not have to infer either convention.

Use deterministic conversion in scientific workflows

MJD appears in astronomy tables, satellite products, observatory logs, and other datasets where a compact continuous day count is easier to compare than formatted civil timestamps. This converter is useful at the boundary where people or general-purpose systems need to read those values. A data ingestion job can convert an MJD column before indexing observations; a researcher can verify a published epoch; and a support engineer can translate a timestamp while investigating a telemetry record. Because the implementation uses integer calendar arithmetic rather than the host's date library, the same input produces the same result in a browser, an API worker, or a test runner in another timezone. That property also makes saved examples reliable regression checks. Treat UTC as the output convention, not as evidence that every source used a perfect physical realization of UTC: specialized datasets may label their day count with TT, TAI, or another time scale. If leap-second-level precision matters, confirm the source scale and apply the appropriate domain correction before interpreting the timestamp. For ordinary MJD values already specified in UTC, the returned fields are ready to store or display.