Julian Date Calculator

Work out julian date instantly with clear inputs, formula shown and shareable results.

About Julian Date Calculator

The Julian date counts days continuously from noon on 1 January 4713 BC, which removes all calendar irregularities from astronomical calculations. 1 January 2026 at 12:00 UT is JD 2461042.0. The modified form subtracts 2400000.5 to give smaller numbers starting at midnight, and days since J2000.0 is the epoch most modern ephemerides use.

Formulas

Julian date

JD = Unix days + 2440587.5 + hour / 24

Modified Julian date

MJD = JD - 2400000.5

Worked example

With the default values below, Julian Date Calculator returns Julian Date of 2,461,042.0000. Change any input above and every figure here is recalculated in your browser.

Inputs used

Calendar date: 2026-01-01
Universal timeaccepts 0–23.999 h: 12 h

Results

Julian Date: 2,461,042.0000 days
Modified Julian Date: 61,041.5000
Day Of The Year: 1
Days Since J2000.0: 9,497.0000

Step by step

1Values used
2Julian date
3Modified Julian date
4Julian Date= 2,461,042.0000 days
5Modified Julian Date= 61,041.5000
6Day Of The Year= 1
7Days Since J2000.0= 9,497.0000

Assumptions and limits

The result is derived only from the 2 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
Figures are rounded for display to 4 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

Why does the Julian day start at noon?

So that a night's observing session falls within a single Julian day, which was convenient before electronic records.

What is J2000.0?

The standard epoch, JD 2451545.0 - 1 January 2000 at 12:00 TT. Star coordinates and orbital elements are referred to it.