Julian Date Calculator
Convert a timestamp to a UTC-based Julian date using the stated civil-time approximation.
Result for the values shown.
Calculations run in your browser.
What to enter
| Input | Meaning and units |
|---|---|
| Instant | Include seconds and an explicit Z or UTC offset, for example 2024-01-01T12:00:00Z. At most three fractional-second digits. |
Understanding your result
Julian date is a continuous day count with a noon boundary, rather than an ordinary calendar day-of-year. The stated UTC approximation is distinct from dynamical astronomical timescales.
Common mistakes
- Confusing Julian date with an ordinal day or treating the UTC approximation as a different timescale.
Check your calculation
- Compare the stated epoch example and remember the noon versus midnight boundary.
Calculation checks, sources and review limits
What is the UTC-based Julian date for this timestamp?
Convert a timestamp to a UTC-based Julian date using the stated civil-time approximation.
Common uses
- Convert a timestamp to a UTC-based Julian date using the stated civil-time approximation.
How it works
JD=UnixSeconds/86400+2440587.5 Calendar arithmetic uses the proleptic Gregorian calendar. Explicit calendar dates are independent of local daylight-saving changes. Month/year additions clamp to the last valid day of the destination month. Timestamp arithmetic requires a stated UTC offset and excludes leap seconds.
Worked example
Enter Instant: 2000-01-01T12:00:00Z. The result is Julian date: 2451545.
FAQ
What is the UTC-based Julian date for this timestamp?
JD=UnixSeconds/86400+2440587.5 Calendar arithmetic uses the proleptic Gregorian calendar. Explicit calendar dates are independent of local daylight-saving changes. Month/year additions clamp to the last valid day of the destination month. Timestamp arithmetic requires a stated UTC offset and excludes leap seconds.
What assumptions and limits apply?
Julian date begins at noon; UTC-based civil conversion differs from dynamical timescales. State UTC approximation.