Is my input uploaded?

No. This website tool runs in your browser. Only the optional public API version sends input to the authenticated API route.

Can I use this in an application?

Yes. The Developers documentation lists the authenticated endpoint, request parameters and response example.

Should I verify the result?

Yes. Deterministic tools are designed for repeatable results, but format-specific or heuristic output should still be checked for your use case.

Date & Time Calculators

Julian Day Calculator

Convert an ISO date and time to Julian Day and Modified Julian Day values.

Free foreverRuns in your browserNo sign-up

UTC date and time

Result

Enter your values and select calculate julian day.

About the Julian Day Calculator

Julian Day Calculator is a focused browser-based utility. Convert an ISO date and time to Julian Day and Modified Julian Day values.

The calculation runs locally in your browser, so the supplied value is not uploaded to ToolsOnDuty. The same capability is also available through the authenticated developer API.

Key features

Fast local processing with explicit validation
Copy-ready structured result
No account, upload or paid data provider required

How to use

1Enter an ISO-compatible date and time.
2Choose any available conversion or formatting options.
3Run the tool and review Julian Day, Modified Julian Day and UTC ISO time.

Examples

Julian Day Calculator example

Input: an ISO-compatible date and time

Output: Julian Day, Modified Julian Day and UTC ISO time

Frequently asked questions

Is my input uploaded?: No. This website tool runs in your browser. Only the optional public API version sends input to the authenticated API route.
Can I use this in an application?: Yes. The Developers documentation lists the authenticated endpoint, request parameters and response example.
Should I verify the result?: Yes. Deterministic tools are designed for repeatable results, but format-specific or heuristic output should still be checked for your use case.