Julian Date Converter
Convert dates to Julian dates both ways: the YYDDD day-of-year code used on packaging and by the military, and the astronomical Julian Date (JD and MJD).
Day of year on the 1st of each month
| Month | Common year | Leap year |
|---|---|---|
| January 1 | 001 | 001 |
| February 1 | 032 | 032 |
| March 1 | 060 | 061 |
| April 1 | 091 | 092 |
| May 1 | 121 | 122 |
| June 1 | 152 | 153 |
| July 1 | 182 | 183 |
| August 1 | 213 | 214 |
| September 1 | 244 | 245 |
| October 1 | 274 | 275 |
| November 1 | 305 | 306 |
| December 1 | 335 | 336 |
What Julian Date Converter Does
“Julian date” means two different things, and this converter handles both. On food packaging, in manufacturing, and in military and government records, it usually means an ordinal date: the year followed by the day of the year, such as 26267 or 2026267 for September 24, 2026. In astronomy it means the Julian Date (JD), a continuous count of days since noon UTC on January 1, 4713 BC: 2461308.0 for noon on the same day.
Today’s value in each form appears as soon as the page loads. Pick any date to convert it, or type a code or a JD to convert it back to a calendar date, including the short one-digit year codes stamped on egg cartons and lot numbers. The astronomical mode also gives the Modified Julian Date and accepts a time of day in UTC.
How to Use Julian Date Converter
- Choose the day-of-year (YYDDD) form or the astronomical Julian Date
- Pick a calendar date; today is filled in automatically
- Read the Julian date, or the JD and MJD with a time in UTC
- Type a code like 26267 or a JD to convert it back to a date
- Use the month table to find day numbers by hand
Formula Used by Julian Date Converter
Ordinal (YYDDD) date
Julian date = last two digits of the year + day of year (001–366)
Worked example
September 24, 2026.
- 243 days before September (31+28+31+30+31+30+31+31)
- 243 + 24 = day 267
Result: 26267, or 2026267 with a four-digit year.
Astronomical Julian Date
JD = ⌊365.25(Y + 4716)⌋ + ⌊30.6001(M + 1)⌋ + D + B − 1524.5 (Meeus), with January and February counted as months 13 and 14 of the previous year
Worked example
January 1, 2000, 12:00 UTC.
- Y = 1999, M = 13, B = −13
- Evaluate the terms
Result: JD 2451545.0 (the J2000.0 epoch); MJD 51544.5.
Reference Epochs
| Date (UTC) | Julian Date | Modified Julian Date |
|---|---|---|
| Nov 17, 1858, 00:00 | 2400000.5 | 0 |
| Jan 1, 1970, 00:00 (Unix epoch) | 2440587.5 | 40587 |
| Jan 1, 2000, 12:00 (J2000.0) | 2451545.0 | 51544.5 |
| Jan 1, 2026, 00:00 | 2461041.5 | 61041 |
How to Read Your Result
Reading food codes
An ordinal code usually marks when a product was made or packed, not when it expires. Egg cartons in the U.S., for example, often show the pack date as a three-digit day of the year, with the sell-by or best-by date printed separately. Manufacturers use their own formats, so the letters and digits around the date vary.
Why astronomers count days
A single running day count makes it easy to find the time between two observations (just subtract) without worrying about months, leap years or calendar reforms. Starting days at noon kept a whole night’s observations under one date for European astronomers.
Limitations & Accuracy Notes
- Astronomical conversions are for dates from October 15, 1582 (the Gregorian calendar) onward.
- Two-digit year codes are read with the usual pivot: 00–68 as 2000–2068, 69–99 as 1969–1999.
- Times are in UTC; convert local time before entering.
Frequently Asked Questions
What is today’s Julian date?
The page shows it when it loads, in both common forms. In the day-of-year form, September 24, 2026 is 26267 (YYDDD) or 2026267 (YYYYDDD): year 2026, day 267 of the year.
What is a Julian date on food packaging?
Many manufacturers print a production or pack date as a year digit or two followed by the day of the year. 26045 would be the 45th day of 2026, February 14. Enter the code to decode it; single-digit year codes are read as the current decade.
What is the astronomical Julian Date?
A continuous count of days since noon Universal Time on January 1, 4713 BC in the Julian calendar, used in astronomy and satellite tracking. J2000.0 (noon UTC on January 1, 2000) is JD 2451545.0.
What is the Modified Julian Date?
MJD = JD − 2,400,000.5. It starts at midnight rather than noon and has fewer digits, which is why it is used by many scientific and space agencies. JD 2451545.0 is MJD 51544.5.
Why is it called a Julian date?
The astronomical count was proposed by Joseph Scaliger in 1583 and is based on the Julian period, not on Julius Caesar directly. The packaging “Julian date” borrows the name loosely; it is properly called an ordinal date.
How do leap years change the day number?
From March 1 on, every day number in a leap year is one higher: March 1 is day 60 in a common year and day 61 in a leap year. The table on this page lists the first day of each month for both.