EpochLab

Julian Day Number Calculator

Work out a Julian Day Number

The 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.

Questions people ask

The things that come up about julian day number calculators, answered plainly.

What is the difference between JD and JDN?

The Julian Date carries a fraction for the time of day; the Julian Day Number is the integer part, naming the whole day that began at the preceding noon. JD 2460508.25 is 18:00 on JDN 2460508.

What is Rata Die?

Days since 1 January 1 CE in the proleptic Gregorian calendar — a fixed count used in calendrical software because it puts day 1 somewhere comprehensible. The Lilian day number does the same from the Gregorian reform in 1582.

Related tools

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

Julian Date ConverterThe 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.
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.
Day of Week CalculatorThe weekday for any date, past or future, plus its week number, day of the year, and which weekday that date falls on in the surrounding years.
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.

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