Converter · Batch
Bulk Julian Date Converter
Paste a whole column of dates or Julian codes — one per line — and convert them all at once. Copy the table or download it as CSV. Everything runs in your browser; nothing is uploaded.
| Input | Calendar date | Weekday | YYYYDDD | YYDDD | Day of year | JD | MJD | Interpretation |
|---|
How the bulk converter works
Each line is treated as one value. In Auto-detect mode the
tool decides what each unambiguous line is: an ISO or slash-formatted
value is read as a calendar date; a plain 3- or 5-digit number is read as
a day-of-year code; and a decimal number is read as JD or MJD. A 7-digit
whole number can validly be either YYYYDDD or an astronomical
JD, so the tool asks you to select a mode instead of making a dangerous
guess.
The astronomical values use the Jean Meeus algorithm and are the same ones produced by the single-value converter. For one date at a time, or to decode a product code, use the Julian date → calendar tool.
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Frequently asked questions
What can I paste into the bulk converter?
One value per line. It accepts calendar dates in ISO form (YYYY-MM-DD), Julian day-of-year codes (7-digit YYYYDDD, 5-digit YYDDD or 3-digit DDD), and astronomical Julian Dates or Modified Julian Dates. A 7-digit whole number is inherently ambiguous, so select Julian-code or JD mode for those values instead of Auto-detect.
How do I convert a spreadsheet column of dates to Julian dates?
Copy the column from Excel or Google Sheets, paste it into the box, keep the mode on “Calendar dates → Julian”, and click Convert. Then use “Download CSV” and paste the result back into your sheet.
Is my data uploaded anywhere?
No. Every line is converted locally in your browser with JavaScript. Nothing you paste is sent to a server, logged or stored.
How are two-digit years handled?
A 5-digit YYDDD code uses the POSIX pivot: 00–68 map to 2000–2068 and 69–99 map to 1969–1999. Use the unambiguous 7-digit YYYYDDD form when you can.