Julian Date Calendar: Day-of-Year Numbers Explained
A Julian date is the day-of-year number: 001 on January 1, counting up to 365, or 366 in a leap year, on December 31. A “Julian date calendar” is a reference table that maps every calendar date to its day-of-year number. Factories, food producers, and logistics teams use it for lot codes and expiration stamps because a single number is quicker to print and scan than a full date.
Three things called “Julian” (and which one you want)
The word “Julian” attaches to three different ideas, and searches for a “Julian date calendar” almost always mean the first one.
- Ordinal date (day-of-year): the 1 to 365/366 count used on packaging and in business systems. This is the everyday “Julian date.”
- Julian Day Number (JDN): an astronomer's continuous count of days since January 1, 4713 BC, used in science and software. Today's JDN is a seven-digit number.
- Julian calendar: the calendar introduced by Julius Caesar in 45 BC, replaced by the Gregorian calendar we use now.
This guide covers the first one, the day-of-year number.
How to read a Julian date code
Manufacturers often print a five-digit code in the form YYDDD: two digits for the year and three for the day of the year. A carton stamped 26100 was made on day 100 of 2026, which is April 10. Some systems drop the year and print only the three-day portion, so 100 alone still means the 100th day. Food producers use these codes for freshness tracking, which is why you see them on eggs, canned goods, and bottled drinks.
Day-of-year reference table
The day-of-year number for the first of each month is fixed, so you can add the day of the month to find any date. For example, March 1 is day 60, so March 15 is day 74 in a common year.
| Month 1st | Common year | Leap year |
|---|---|---|
| January 1 | 1 | 1 |
| February 1 | 32 | 32 |
| March 1 | 60 | 61 |
| April 1 | 91 | 92 |
| 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 |
Why leap years shift the numbers
Up to the end of February the day-of-year numbers are identical in every year. From March 1 onward, a leap year is one day ahead because February 29 has been added. That is why December 31 is day 365 in a common year and day 366 in a leap year. The leap-year rule itself decides which years get the extra day. If you work with Julian dates across a leap year, use the leap column for any date from March onward.
How to convert a date to its Julian date
To convert by hand, take the day-of-year number for the first of the month from the table above and add the day minus one. For September 20 in a common year: day 244 for September 1, plus 19, gives day 263. To go the other way, find the largest first-of-month number at or below your Julian date, then count forward. For a calendar you can print with any year's dates laid out in full, open the PrintAnyCalendar generator and download a free PDF. If you are new to printing PDFs at the right paper size, see how to print a calendar PDF.
Frequently asked questions
Is a Julian date the same as the day of the year?
Yes. In everyday and industrial use, “Julian date” means the ordinal day of the year, 1 through 365 or 366. The astronomical Julian Day Number is a separate, much larger count.
What is today's Julian date?
Count the days from January 1 through today, including both. Use the first-of-month table above: add the day of the month to the first-of-month value, then subtract one.
What does a 5-digit Julian date like 26075 mean?
The first two digits are the year (2026) and the last three are the day of the year (075), which is March 16, 2026.
Do Julian dates reset each year?
Yes. The count restarts at 1 on January 1 every year, which is why the year prefix is added in lot codes.
Julian Day Number definitions follow the US Naval Observatory.