Julian Date Converter
Choose what you have: a calendar date and time, a Julian date number, or a day of year code such as 26291. The other forms appear straight away.
Times are in UTC (Coordinated Universal Time). The Julian date counts days from noon on 1 January 4713 BC in the Julian calendar.
Worked examples
The year 2000 reference
1 January 2000 at 12:00:00 UTC
Julian date 2451545.00000
A standard reference point for astronomy.
Day of year code
18 October 2026
2026291 (or 26291)
Day 291 of 365.
Julian calendar
18 October 2026
5 October 2026
13 days behind.
About Julian Date Converter
The word Julian is used for three different things. Astronomers use the Julian date, a continuous count of days and fractions of a day, so that events can be timed without months or time zones. Factories, warehouses and the armed forces often write a Julian date as the year and day of the year, such as 26291 for 18 October 2026. And the Julian calendar is the old calendar that the Gregorian one replaced. This converter handles all three and shows them together.
Choose what you have. Enter a calendar date and a time in UTC to get the Julian date, the Julian day number, the modified Julian date used in satellite and space work, both day of year codes and the matching date in the Julian calendar, which is 13 days behind in this century. Or enter a Julian date number, or a five or seven digit day of year code, to get the calendar date back. The Julian day changes at noon UTC, which is why 12:00 on 1 January 2000 is exactly 2451545.0.
How to use Julian Date Converter
- Choose whether you have a date and time, a Julian date number or a day of year code.
- Enter the value. Times are in UTC.
- Read the Julian date, the day number and the modified Julian date.
- Use the day of year codes for forms and labels that ask for them.
Common uses
- Reading the date code on a food or manufacturing batch
- Converting dates for astronomy or satellite data
- Converting old records dated in the Julian calendar
- Turning a YYDDD code from a system into a calendar date
Frequently asked questions
What is the Julian date for today?
Enter today's date and the time in UTC. For noon UTC on 18 October 2026 the Julian date is 2461332.0.
What does a code like 26291 mean?
It is the year 2026 and day 291 of that year, which is 18 October. Two digit years are read as 2000 to 2099.
What is the modified Julian date?
It is the Julian date minus 2,400,000.5, so that the day starts at midnight and the numbers are shorter.
How far behind is the Julian calendar?
In the years 1900 to 2099 it is 13 days behind the Gregorian calendar. 18 October 2026 is 5 October in the Julian calendar.
Why is there a half in the Julian date?
The count begins at noon, so midnight falls halfway through a Julian day and ends in .5.