Time & dates
Julian date calculator
Turn a calendar date into its day-of-year number and the 5-digit YYDDD code, or convert an ordinal day back to a date.
The YYDDD code takes the last two digits of the year and the three-digit day of the year, so 24 April 2026 is 26114.
How the ordinal day and YYDDD code are worked out
The ordinal day, often called the Julian day in industry, is the count of days from 1 January to your date inclusive: 1 January is day 1 and 31 December is day 365, or day 366 in a leap year. The calculator adds up the lengths of the whole months before your month and then adds the day of the month. For 10 April 2026 that is 31 + 28 + 31 (January to March) + 10 = day 100. The five-digit code pairs the last two digits of the year with the three-digit day: 2026 day 100 becomes 26100, which is the stamp you see on food packaging, egg cartons and aircraft parts.
The reverse works the same way backwards: give the year and an ordinal day, and the tool steps forward from 1 January by that many days minus one. Day 100 of 2026 lands back on 10 April. Leap years matter here, because day 60 is 1 March in a normal year but 29 February in a leap year such as 2028.
| Date | Ordinal day | YYDDD | Leap year |
|---|---|---|---|
| 1 Jan 2026 | 1 | 26001 | No |
| 28 Feb 2026 | 59 | 26059 | No |
| 1 Mar 2026 | 60 | 26060 | No |
| 1 Mar 2028 | 61 | 28061 | Yes |
| 31 Dec 2026 | 365 | 26365 | No |
Where ordinal dates are used
This day-of-year number is not the astronomical Julian Day used by astronomers, which counts days continuously from 4713 BC; it simply numbers the days within one year. Manufacturers favour it because a batch stamp like 26114 is compact, sorts cleanly and dodges the month-order confusion between formats like 04/11 and 11/04. Aviation and the military use the same YYDDD idea for serials and ration packs. A common trap is the leap year: code 26366 cannot exist because 2026 has only 365 days, while 28366 is valid because 2028 is a leap year. Another is assuming two digits for the year are enough forever, which is why some systems have moved to a four-digit YYYYDDD form for records that must span decades.
Frequently asked questions
What is a Julian date on a product label?
It is usually the ordinal day of the year, sometimes with the year in front. A stamp of 26114 means the 114th day of 2026, which is 24 April 2026, not the 1st to 14th of any month.
Is the ordinal day the same as the astronomical Julian Day?
No. The ordinal day runs 1 to 366 within a single year. The astronomical Julian Day is a running count of days since 4713 BC and reaches over 2.4 million, so the two numbers are unrelated.
How do I read a 5-digit Julian code like 26095?
Split it into the year and the day: 26 is 2026 and 095 is the 95th day, which is 5 April 2026. The first two digits are the year, the last three the day of the year.