Reference
Julian Date FAQ
Straight answers to the questions people actually ask about Julian dates — both the manufacturing day-of-year code and the astronomical day count.
What is today’s Julian date?
It depends on which "Julian date" you mean. In manufacturing and IT it is the day-of-year format — the last three digits are the day number from 001 to 365 (or 366 in a leap year), usually prefixed by the year, e.g. 2026202 or 26202. In astronomy it is the continuous Julian Date, a running count of days that today sits in the 2,461,000s. The live figures at the top of this page show both for the current moment.
Why does "Julian date" mean two different things?
They come from two unrelated traditions that ended up sharing a name. The astronomical Julian Date was defined in 1583 by Joseph Scaliger as a single continuous day count for astronomers. Separately, business and government systems began calling the ordinal "day of year" a "Julian date" because it was convenient for punch cards and mainframes. Both are in everyday use, so a good tool has to handle each.
How do I read a Julian date on a product or package?
Most packaged-goods codes use the ordinal format. A 5-digit code like 26202 breaks down as the year (26 → 2026) followed by the day of year (202 → July 21). A 4- or 3-digit code is often just the day of year for the current year. Paste the code into the converter to decode it instantly.
Is the Julian date the same as the Julian calendar?
No. The Julian calendar is the old solar calendar introduced by Julius Caesar in 45 BC and replaced by the Gregorian calendar from 1582. The astronomical Julian Date is a day count that is only named after that calendar because its starting epoch is defined in it. The ordinal "day of year" Julian date has nothing to do with Julius Caesar at all.
What is the Modified Julian Date (MJD)?
The Modified Julian Date is the astronomical Julian Date minus 2,400,000.5. The half-day shift makes the MJD roll over at midnight instead of noon, and the smaller number is easier to store. It is widely used in satellite tracking, geodesy and computing.
Does the Julian date change at midnight or noon?
The ordinal day-of-year Julian date changes at local midnight, like any calendar date. The astronomical Julian Date, by definition, increments by a whole number at 12:00 noon Universal Time — which is why "now" almost always has a .5-ish fractional part rather than a round number.
How do I find the Julian date of a specific past or future date?
Use the converter: choose "Calendar date", enter the month, day and year, and read off the day-of-year code and the astronomical Julian Date. For a whole year at a glance, open that year’s printable calendar.
What is the Julian date used for on eggs and food packaging?
It records the day the product was packed or produced. On USDA-graded eggs, a 3-digit Julian date (001–365) is printed near the sell-by date and marks the pack day. On many canned goods and MREs, a 4- or 5-digit code adds the year. It is a production date, which helps with rotation and recalls — not necessarily an expiry date.
Is a Julian date the same as an ISO ordinal date?
Effectively yes, for the day-of-year meaning. ISO 8601 defines the "ordinal date" as YYYY-DDD (for example 2026-202). The industrial Julian date is the same day-of-year value, usually written without the hyphen. The astronomical Julian Date is a completely different, continuous count.
How many digits should a Julian date have?
The day-of-year form has 3 digits (day only), 5 digits (YYDDD) or 7 digits (YYYYDDD). The astronomical Julian Date currently has 7 digits before the decimal point (around 2.46 million), and the Modified Julian Date has 5 digits (around 60,000).
What is the Julian Day Number for today?
The Julian Day Number (JDN) is the whole-day astronomical count and today it is in the 2,461,000s. The exact value is shown live on the home page and in the astronomical converter.
Why do two-digit-year Julian dates cause problems?
A 5-digit YYDDD code can be ambiguous: "26202" could mean 2026 or 1926. Systems resolve this with a pivot year — here, 00–68 map to the 2000s and 69–99 to the 1900s. Whenever possible, use the unambiguous 7-digit YYYYDDD form.