Does Julian Day Number upload my file or text to Tool-You servers?

No. Julian Day Number runs in this browser tab. Files stay on the device. Limit note: Local YMD → integer JDN and MJD. Invalid dates fail.

Should I use Unix Timestamp Converter instead of Julian Day Number?

Use Julian Day Number when you need Gregorian date to JDN and Modified Julian Day. Use Unix Timestamp Converter when you need Unix seconds/millis ↔ date, with timezone display. They share a category (Date & time) but not the same job.

Julian Day Number

Gregorian date to JDN and Modified Julian Day.

Converts a local YMD to Julian Day Number at noon UTC and MJD = JDN − 2400000.5. Unlike Unix Timestamp this is not seconds since 1970. Unlike Day of Year this is not 1–366 inside one year. Invalid dates fail.

What Julian Day Number does

Practical limit for Julian Day Number: Local YMD → integer JDN and MJD. Invalid dates fail. That is why output can differ from heavy desktop Date & time software. Read the tool-specific note again: Converts a local YMD to Julian Day Number at noon UTC and MJD = JDN − 2400000.5. Unlike Unix Timestamp this is not seconds since 1970. Unlike Day of Year this is not 1–366 inside one year. Invalid dates fail.

How to use Julian Day Number

Confirm you need Julian Day Number, not Unix Timestamp Converter (Unix seconds/millis ↔ date, with timezone display.). Address: /datetime/julian-day.
Enter the numbers or dates Julian Day Number uses. Gregorian date to JDN and Modified Julian Day.
Read the result as Julian Day Number defines it — not as Day of Year (Ordinal day 1–366 plus remaining days in the year.). Converts a local YMD to Julian Day Number at noon UTC and MJD = JDN − 2400000.5. Unlike Unix Timestamp this is not seconds since 1970. Unlike Day of Year this is not 1–366 inside one year. Invalid dates fail.
Julian Day Number is an estimate in the browser, not professional advice. Local YMD → integer JDN and MJD. Invalid dates fail.
Need a different formula? Try Day of Year (Ordinal day 1–366 plus remaining days in the year.) instead of stretching Julian Day Number.

When not to use Julian Day Number

Skip Julian Day Number when a neighbor tool matches better — start with Unix Timestamp Converter or Day of Year — or when the description already warns the job will fail. In the tool’s own words: Converts a local YMD to Julian Day Number at noon UTC and MJD = JDN − 2400000.5. Unlike Unix Timestamp this is not seconds since 1970. Unlike Day of Year this is not 1–366 inside one year. Invalid dates fail.

Questions about Julian Day Number

What does Julian Day Number do that other Date & time pages on this site do not?: Converts a local YMD to Julian Day Number at noon UTC and MJD = JDN − 2400000.5. Unlike Unix Timestamp this is not seconds since 1970. Unlike Day of Year this is not 1–366 inside one year. Invalid dates fail. Short version: Gregorian date to JDN and Modified Julian Day.
Does Julian Day Number upload my file or text to Tool-You servers?: No. Julian Day Number runs in this browser tab. Files stay on the device. Limit note: Local YMD → integer JDN and MJD. Invalid dates fail.
Should I use Unix Timestamp Converter instead of Julian Day Number?: Use Julian Day Number when you need Gregorian date to JDN and Modified Julian Day. Use Unix Timestamp Converter when you need Unix seconds/millis ↔ date, with timezone display. They share a category (Date & time) but not the same job.
What are the limits of Julian Day Number?: Local YMD → integer JDN and MJD. Invalid dates fail. Also: Converts a local YMD to Julian Day Number at noon UTC and MJD = JDN − 2400000.5. Unlike Unix Timestamp this is not seconds since 1970. Unlike Day of Year this is not 1–366 inside one year. Invalid dates fail.