Julian Date Converter — Calendar Dates and Day Numbers
Convert standard calendar dates into ordinal Julian codes, short production codes, and astronomical Julian day values. Reverse the ordinal format when you need the Gregorian date back.
Julian Date
Understand the difference between ordinal Julian formats and astronomical Julian day numbers, convert between formats, and browse reference charts by year.
Use the converter
The widget covers the common industrial format and the astronomical count in one place.
Worked examples
Examples make the format differences easier to spot than a bare formula does.
| Calendar date | ISO | Ordinal Julian | Short code | JDN | JD |
|---|---|---|---|---|---|
| Thursday, January 15, 2026 | 2026-01-15 | 2026-015 | 26015 | 2461056 | 2461055.50000 |
| Tuesday, June 9, 2026 | 2026-06-09 | 2026-160 | 26160 | 2461201 | 2461200.50000 |
| Thursday, December 31, 2026 | 2026-12-31 | 2026-365 | 26365 | 2461406 | 2461405.50000 |
What this page converts
The ordinal format writes a date as year plus day-of-year, such as 2026-015. The five-digit production version drops the century and becomes 26015. Those are the forms most often used on labels, batch codes, and operational checklists.
The astronomical system is different: it counts days continuously from a fixed epoch and is most useful in astronomy, orbital mechanics, and historical chronology. By keeping both outputs together, the converter handles the ambiguity that makes many “Julian date” search results confusing.
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Check the conversion against the source
Choose the intended Julian system
Use the calendar input for a known Gregorian date or enter a year and ordinal day to decode an ordinal value. Preserve all three day digits in saved codes. The maximum is 365 for a common year and 366 for a leap year.
The astronomical output describes a day count at the time represented by the date input. Check whether that reference time is local midnight or UTC before comparing a fractional Julian date from another source.
A reliable production-code workflow
First identify the year field and the day field in the issuer’s format. Next confirm whether the year is a leap year. Convert the ordinal day, then check a neighboring known record to confirm that the interpretation makes sense.
Two-digit years lose the century. For durable records, store a four-digit year alongside the original code. A converter cannot recover missing century information or tell which product-specific suffix is part of a date.
Day 060 of 2024 is February 29. Day 060 of 2026 is March 1. If a conversion is off by one after February, check the selected year first.
A common mistake to avoid
Astronomical calculations may use different time scales. This tool’s JD follows JavaScript’s UTC-style timestamp arithmetic.