About the Julian Date Converter
The Julian Date counts days continuously, with no months or years, from noon on 1 January 4713 BC. Astronomers use it to time observations, because subtracting two Julian Dates gives the time between them in days. This tool converts a date and a UTC time to the Julian Date, the Modified Julian Date, and the days since the Unix epoch, and converts a Julian Date back to a date and time. Type a date and UTC time, or a Julian Date and the Julian Date appears at once, with a few related figures underneath, and you can copy the result with one tap. The sums run in your browser, so nothing you enter is uploaded.
Updated October 2026
How to use the Julian Date Converter
- 1Enter a date and UTC time, or a Julian Date.
- 2Pick the units or options from the menus if the Julian Date tool offers them.
- 3Read the Julian Date in the large result box.
- 4Look at the extra rows for related figures.
- 5Press Copy result to keep the answer.
When you need the Julian Date
Astronomers, satellite trackers and some data loggers use Julian Dates. Programmers use them to compute the difference between dates exactly, and historians use them to compare dates from different calendars.
The Julian Date should not be confused with the Julian calendar, the old Roman calendar, or with the day of the year, which people sometimes call the Julian day. These are different things.
How the Julian Date is worked out
Julian Date = days since 1970-01-01 + 2,440,587.5 (where the days include the fraction of the day). Modified Julian Date = JD − 2,400,000.5. Noon UTC on 1 January 2000 is JD 2,451,545.0 and MJD 51,544.5. The Unix epoch, midnight on 1 January 1970, is JD 2,440,587.5. A JD of 2,461,318.25 is 18:00 UTC on 4 October 2026.
Every answer on this page comes from that one rule, so you can check any result by hand with a calculator. The figures shown underneath, such as other units, are conversions of the same answer.
- JD, MJD and Unix days
- Both directions
- UTC based
Mistakes to avoid with Julian Date
A Julian Date begins at noon, not midnight, so the date changes at 12:00 UT. The tool uses UTC times and the Gregorian calendar, and it covers the years 1 to 9999. Enter the hour as 0 to 23.
On phone and computer
On a phone, type into the boxes one after another and read the Julian Date underneath; Copy result puts it on the clipboard for a message or a note. On a computer the inputs sit on the left and the answer on the right, so you can change one figure and watch the Julian Date move. The julian date converter works the same on both. Date systems differ, so cross-check with others. Convert machine times with the Unix Timestamp Converter, find the ordinal day with the Day of the Year Calculator, and count the gap between two days with Days Between Dates.
Features
- Day starts at noon
- Not the Julian calendar
- UTC times only
- Clear messages when the Julian Date inputs make no sense
- Copy the result with one tap
- Private: nothing is uploaded
Frequently asked questions
How do I calculate Julian Date?
Julian Date = days since 1970-01-01 + 2,440,587.5 (where the days include the fraction of the day). Modified Julian Date = JD − 2,400,000.5. Noon UTC on 1 January 2000 is JD 2,451,545.0 and MJD 51,544.5. The Unix epoch, midnight on 1 January 1970, is JD 2,440,587.5. A JD of 2,461,318.25 is 18:00 UTC on 4 October 2026.
What is the formula for Julian Date?
Julian Date = days since 1970-01-01 + 2,440,587.5 (where the days include the fraction of the day). Modified Julian Date = JD − 2,400,000.5. The julian date converter applies it exactly and rounds only the displayed answer to six significant figures.
Why does the Julian Date start at noon?
Astronomers worked at night and wanted the date to stay the same through a whole night of observing.
What is the Modified Julian Date?
JD minus 2,400,000.5, which makes the number smaller and starts the day at midnight.
Is it the same as the Julian calendar?
No. The Julian calendar is the old calendar used before the Gregorian one.
Is this julian date converter free and private?
Yes. It is free, needs no account and runs in your browser, so the numbers you type are not uploaded or stored.