How to use Julian Date Converter
Get the best out of Julian Date Converter: every option explained, a worked example, and what to check when the output is not what you expected.
Updated July 31, 2026
What it does
Convert between calendar dates and astronomical Julian day numbers. It runs entirely in your browser — your input never leaves your device.
Options
Every setting this tool exposes, straight from the code that validates it.
| Option | Type | Default | What it does |
|---|---|---|---|
mode | one of: date-to-julian, julian-to-date | date-to-julian | Defaults to date-to-julian. |
date | text | — | Date/time (for date-to-julian). |
julian | number | — | Julian day number (for julian-to-date). |
Example
Try it with these settings on the tool page:
mode:date-to-julian
Getting the result you want
Most of the control here is in the options above. If the output is not what you expected, the setting to check first is mode and date — those change the shape of the output rather than the input it accepts.
Troubleshooting
- It is slow on very large input. Everything runs in your browser, so speed depends on your device. Very large inputs are best split up, or run through the API where the work happens on our servers.
Automating it
The same logic is available as a REST endpoint, so you can run it from a script, a CI job or your own app.
Bashcurl "https://api.toolsxpo.com/v1/julian-converter" \ -H "Authorization: Bearer $TOOLSXPO_KEY"
It costs 1 credit per successful call. See the full endpoint reference, or try it in the playground.
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