Julian Date Calendar Converter
Bidirectional conversion between Gregorian calendar and Julian Date (JD), Modified Julian Date (MJD), and Day of Year
Compute astronomical time scales and supply chain tracking days instantly. Supports real-time monitoring and custom epoch mappings.
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🔒 Everything runs 100% in your browser. Your files and input are never uploaded to any server.
How to use
- Input a Gregorian calendar date to get JD, MJD, and the exact Day of the Year.
- Alternatively, input a custom decimal Julian Date to reverse-calculate the calendar timestamp.
- Use the top active banner to observe the current flowing Julian time live.
FAQ
- What is a Julian Date?
- A continuous count of days since the beginning of the Julian Period (January 1, 4713 BC at noon UTC). It allows astronomers to calculate temporal intervals using simple arithmetic.
- What is the difference between JD and MJD?
- Modified Julian Date (MJD) offsets JD by subtracting 2400000.5. MJD starts days at midnight instead of noon, making it more intuitive for civil and computing systems.
- Does the converter give accurate results for dates before the 1582 Gregorian calendar reform?
- This tool uses the proleptic Gregorian calendar, meaning it projects today's calendar rules backward in time for simplicity. For dates before October 15, 1582, this can differ from the Julian calendar actually in use at the time by up to ten days or more, so treat results for ancient historical dates as an approximation and double-check them for serious research.