Julian date converter

Type the number you've found, like `26274` from a food label, `126274` from a JD Edwards report or `2461315` from an astronomy table. The converter works out which kind of number it is, shows the date, and gives the same day in every other format. If the number could be read more than one way, the working says so, and Read a number as picks the one you mean.

It works the other way too. Type a date, like `1 October 2026`, and you get its day of the year, its YYDDD and YYYYDDD codes, its JD Edwards number, Julian Day Number, Excel serial and the date in the Julian calendar. Type `today` for today's.

The name covers three unrelated things. On packaging and in logistics, a Julian date is an ordinal date, the year and then the day of the year: `26274` is the 274th day of 2026, which is 1 October. Some systems write the year in full, `2026274`.

JD Edwards, Oracle's business software, adds a century digit in front: `126274`, where 1 means the 2000s and 0 the 1900s.

Astronomers mean something else entirely, a count of days from 1 January 4713 BC. 1 October 2026 is day 2,461,315. Oracle databases use the same count for their J date format.

Excel stores a date as a count of days. In its usual 1900 system, 1 January 1900 is 1 and 1 January 2025 is 45658, which is why a date column sometimes turns into five-digit numbers. Macs once defaulted to a 1904 system that starts at 0 on 1 January 1904, so a workbook moved between the two can be out by 1,462 days.

The 1900 system also contains a day that never happened. Lotus 1-2-3 treated 1900 as a leap year, and Excel copied it so that spreadsheets would move between the two, which gave 29 February 1900 the serial 60. Microsoft has kept the error, because fixing it would move almost every date in every existing spreadsheet by a day.

Joseph Scaliger set up the astronomers' count in 1583, the year after the Gregorian calendar reform. He chose a starting point where three old cycles lined up: the 28-year solar cycle, the 19-year lunar cycle and the 15-year indiction, which repeat together every 7,980 years. It's often said he named it after his father, Julius Caesar Scaliger. He wrote that he called it Julian because it fits the Julian year. Its days begin at noon, the way astronomers counted them, so a night's observations share one number.