Julian Date Calculator
Convert a date to a Julian date, and back. This page covers both meanings: the day of the year (1 to 365 or 366) and the astronomical Julian Date (JD) used in astronomy.
Two meanings of “Julian date”
- Day of the year: Jan 1 is day 1 and Dec 31 is day 365 or 366. Used in logistics, military, and manufacturing codes, often written YYDDD or YYYYDDD.
- Astronomical Julian Date (JD): the number of days, with decimals, since noon UTC on Jan 1, 4713 BC. Used in astronomy.
Day of the year
318
Check the highlighted fields to see your result.
- Calendar date (UTC)
- Saturday, November 14, 2026 · 00:00:00
- Day of the year
- 318 of 365
- YYDDD · YYYYDDD
- 26318 · 2026318
- Astronomical Julian Date (JD)
- 2461358.50000
- Modified Julian Date (MJD)
- 61358.00000
Results are estimates for information only and do not constitute financial, medical, or legal advice.
Two meanings of Julian date
Day of the year (ordinal date). The number of the day within the year: January 1 is day 1, February 1 is day 32, and December 31 is day 365, or 366 in a leap year. It is often written as a 5-digit code, YYDDD, or a 7-digit code, YYYYDDD.
Astronomical Julian Date (JD). A continuous count of days since noon UTC on January 1, 4713 BC, with the time of day as a decimal. It avoids months and leap years, which makes it handy to find the time between two astronomical events. The Modified Julian Date is JD − 2,400,000.5.
The formulas
Day of the year = days since January 1 of that year + 1
JD = days since January 1, 1970 + 2,440,587.5 (at 00:00 UTC)
Worked example
November 14, 2026 at 00:00 UTC.
- Days before November: 304 (January through October, in a common year). 304 + 14 = day 318.
- As codes: 26318 (YYDDD) and 2026318 (YYYYDDD).
- Astronomical Julian Date: 2461358.5. At noon the same day it would be 2461359.0.
- Check with a known value: January 1, 2000 at 12:00 UTC is JD 2451545.0, the standard epoch J2000.
Frequently asked questions
What is a Julian date?
The term has two common meanings. In logistics, the military, and manufacturing, a Julian date is the day of the year, from 1 to 365 or 366, often written YYDDD or YYYYDDD (for example 26318 for November 14, 2026). In astronomy, the Julian Date (JD) is a continuous count of days, with decimals, since noon UTC on January 1, 4713 BC, and today it is a number around 2.46 million.
What is today's Julian date?
It depends on which one you mean. The calculator opens with today's date: the day of the year, the YYDDD and YYYYDDD codes, and the astronomical Julian Date at 00:00 UTC. Change the date or the time to convert any other moment.
Why does the astronomical Julian Date start at noon?
Astronomers used to work at night, and starting the day at noon kept a whole night of observations within a single date. So midnight UTC has a JD ending in .5, and noon ends in .0. The Modified Julian Date (MJD) subtracts 2,400,000.5 so that it starts at midnight and the numbers are shorter.
Is the Julian date the same as the Julian calendar?
No. The Julian calendar is the old calendar introduced by Julius Caesar that was replaced by the Gregorian calendar from 1582. The Julian dates in this page are day counts. The calculator uses the Gregorian calendar and accepts dates from October 15, 1582.