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UTC date
Convert between calendar dates, Unix epoch time and Julian day numbers.
This converter moves freely between three ways of representing a moment in time: a normal calendar date, a Unix timestamp (the number of seconds since January 1, 1970 UTC used throughout software systems), and a Julian day number (a continuous day count from a fixed historical epoch used in astronomy and some scientific fields). Enter a value in any one of the three formats and the tool fills in the other two along with the full ISO 8601 representation.
Unix time underpins most databases, APIs, logging systems and programming languages, where dates are frequently stored and passed around as a single integer rather than a formatted string. When you're debugging a log file, inspecting an API payload, or writing a script that needs a specific cutoff timestamp, converting between a human-readable date and the raw epoch seconds by hand is slow and error-prone — this tool does it instantly in either direction.
Julian day numbers give astronomers, satellite operators and some scientific computing systems a single continuously incrementing number for any date, which avoids the awkward arithmetic of months and years entirely and makes it trivial to calculate the exact number of days between two arbitrary dates, even across different calendar systems or centuries. It's a different concept from the 'Julian calendar' used historically before the Gregorian reform — this tool uses the Julian Day Number system, which is what's actually used in scientific and astronomical software.
All conversions route through UTC milliseconds internally: a calendar date is treated as midnight UTC on that day, a Unix timestamp is multiplied by 1000 to get milliseconds, and the Julian day number is derived using the standard offset between the Unix epoch and the Julian epoch. This keeps every value internally consistent, so converting a date to a timestamp and back again always returns the original date.
Yes. When converting from a calendar date, the tool treats it as 00:00:00 UTC on that date, which is the standard convention for date-only conversions to timestamp formats.
This tool expects and returns Unix time in seconds, which is the traditional Unix standard. Many JavaScript APIs use milliseconds instead — if you're pulling a timestamp from JavaScript's Date.now(), divide by 1000 before entering it here.
Julian day numbers count from noon, not midnight, so a date at midnight UTC lands on a .5 fraction. The decimal component reflects the time of day within the Julian day convention.
Yes, timestamps before 1970 (negative numbers) are supported and will convert correctly to their corresponding calendar date and Julian day number.
No — this tool uses Julian Day Numbers, a continuous day-counting system used in science and astronomy, which is distinct from the historical Julian calendar (a leap-year system that predates the Gregorian calendar).