EpochLab

Julian Date Converter

Convert a Julian date to a calendar date

The astronomer's continuous day count, both ways — including the half-day offset that catches everyone, since a Julian day begins at noon rather than midnight.

Questions people ask

The things that come up about julian date converters, answered plainly.

What is a Julian date?

A continuous count of days since noon on 1 January 4713 BCE in the proleptic Julian calendar. Astronomers use it because it has no months, no years and no calendar reforms in it — the difference between two Julian dates is simply a number of days.

Why does a Julian day start at noon?

So that a night's observing session falls on one date. Joseph Scaliger set it up that way in 1583, and astronomy has kept it — which is why the Unix epoch is JD 2440587.5 rather than a round number.

Is this the same as a 'Julian date' in a warehouse?

No, and the collision causes real confusion. Manufacturing and logistics often use a five-digit ordinal date — 24198 for the 198th day of 2024 — and call it Julian. That is an ordinal date; this page converts the astronomical one.

Related tools

Julian days, Excel serials, GPS time, cron expressions and format validators.

Julian Day Number CalculatorThe whole-number form — the JD of the noon that starts a day — with the Lilian and Rata Die day counts beside it, which are the same idea from different zero points.
Modified Julian Date ConverterMJD — the Julian date with 2,400,000.5 taken off, so it starts at midnight and fits in five digits. Used in satellite tracking, geodesy and time metrology.
Epoch ConverterThe same conversion as a Unix timestamp, plus the other epochs a number might belong to — Windows FILETIME, .NET ticks, Excel serials, Julian days — ranked by how plausible each reading is.
ISO Date ConverterThe extended form, the basic form, the week date and the ordinal date — all four ISO 8601 shapes for one instant, plus a parser for reading them back.

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