A year and a day number
In a YYYY-DDD code, 2026-015 means the fifteenth day of 2026: January 15. A shortened YYDDD code writes it as 26015. These ordinal codes are often used in production and inventory records.
Julian date reference
Julian Date Today and Julian Date Converter
Read today’s day-of-year code, convert a calendar date, or find an astronomical day count. Check which convention your label or record uses before choosing a result.
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Julian Date
Understand the difference between ordinal Julian formats and astronomical Julian day numbers, convert between formats, and browse reference charts by year.
Today’s Julian date and date conversion
The live code follows your device’s local date. Astronomical JD uses the current instant in UTC.
Enable JavaScript to calculate current Julian values and convert dates. Year charts below work without JavaScript.
Enable JavaScript to calculate current Julian values and convert dates. Year charts below work without JavaScript.
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Two systems share one name
Read the context before the digits
On a production label, “Julian date” often means a year plus the ordinal day within that year. In astronomy, Julian date means a continuous count of days and fractions of a day. The historical Julian calendar is a third, separate concept.
An ordinal code resets at the start of each year. An astronomical day count continues increasing across year boundaries. You cannot convert between them by simply adding a decimal point or dropping some digits.
Decoding a production code
A code such as 26015 may mean day 015 of 2026 in a YYDDD system: January 15. But a manufacturer can use a different year convention, an embedded plant code, or a proprietary lot scheme. Confirm the label specification before interpreting an unfamiliar code.
An ordinal date identifies a production date only if that is what the issuer encodes. It does not establish an expiry date or shelf life. Keep the original code with any decoded date so the interpretation remains traceable.
The noon boundary in astronomy
At 2000-01-01T12:00:00Z, the Julian date is 2451545.0. At midnight at the start of that date, it is 2451544.5. The fractional .5 at midnight is expected.
A common mistake to avoid
Never treat a five-digit lot code as an astronomical Julian day number. Confirm which system the source uses.