Julian Date Converter

Convert a Julian date in either meaning of the term. On food, drug and manufacturing codes a “Julian date” is the day of the year: 27045 means day 45 of 2027, which is 14 February 2027. Type a date to get its YYDDD and YYYYDDD code, or type a code to get the date back; leap years are handled, so 1 March is day 060 in 2027 and day 061 in 2028. In astronomy the Julian Day (JD) is a running count of days since noon on 1 January 4713 BC, and the Modified Julian Date (MJD) starts at midnight on 17 November 1858: convert any date and time to JD and MJD, or a JD or MJD back to a date. Print a day-of-year calendar for 2027 or any year, with every day’s number, as a PDF on US Letter or A4, or download every day as a CSV.

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How to convert a Julian date

1. Read today’s day of the year and code in the box at the top.
2. Pick a date to get its YYDDD and YYYYDDD code, or type a code such as 27045 or 2027045 to get the date.
3. For a two-digit year, choose whether it means 2000–2099 or 1900–1999.
4. For astronomy, type a date and a UT time to get the JD and MJD, or type a JD or MJD to get the date and time.
5. Pick a year and download the day-of-year calendar PDF or the CSV.

What you can use it for

• Reading lot codes and best-before codes on food and drug packaging
• Writing batch and production dates as YYDDD
• Counting days between dates on a day-of-year calendar
• Converting observation times to JD or MJD for astronomy and satellite data
• A printed 2027 day-of-year chart on the wall

2027 day-of-year chart

Month	Days of the year	YYDDD codes	Day 1 in 2028
January	001–031	27001–27031	001
February	032–059	27032–27059	032
March	060–090	27060–27090	061
April	091–120	27091–27120	092
May	121–151	27121–27151	122
June	152–181	27152–27181	153
July	182–212	27182–27212	183
August	213–243	27213–27243	214
September	244–273	27244–27273	245
October	274–304	27274–27304	275
November	305–334	27305–27334	306
December	335–365	27335–27365	336

2027 has 365 days, so the codes run from 27001 (1 January) to 27365 (31 December). In the leap year 2028 every date from 1 March is one day later.

Two meanings of “Julian date”

Ordinal date: the day of the year on the Gregorian calendar, used on food, drug and manufacturing codes and in many computer systems (YYDDD, YYYYDDD, YYYY-DDD). Julian Day: “a continuous count of days and fractions since noon Universal Time on January 1, 4713 BC”, in the words of the US Naval Observatory (read 13 November 2026). The Wikipedia article “Julian day” (read 13 November 2026) notes that the term is also used for the ordinal date, especially in programming, the military and the food industry, which is why ordinal date or day of year is preferred.

Julian Day reference points

Moment (UT)	JD	MJD
1 January 2000, 12:00 (J2000.0)	2451545.0	51544.5
1 January 2027, 00:00	2461406.5	61406
1 January 1970, 00:00 (Unix time 0)	2440587.5	40587
17 November 1858, 00:00 (MJD 0)	2400000.5	0
15 October 1582, 00:00 (first Gregorian day)	2299160.5	−100840

The conversion uses the integer day-number formula of Fliegel and Van Flandern (1968) for Gregorian dates and the matching Julian-calendar formula, as given in the Wikipedia article, and Richards’ algorithm for the reverse; every day from 1900 to 2100 is checked both ways in our tests.

More for dates and planning

• The year on one page, with holidays: 2027 Calendar.
• Any month of any year: Calendar Maker.

Frequently asked questions

What is a Julian date?

The term has two meanings. On product codes, in the military and in programming it usually means the ordinal date, the day of the year from 1 to 365 or 366, written as YYDDD or YYYYDDD. In astronomy it means the Julian Day, a continuous count of days and fractions from noon Universal Time on 1 January 4713 BC.

Is a Julian date the same as the Julian calendar?

No. The Julian calendar is the Roman calendar that the Gregorian calendar replaced from October 1582. Day-of-year codes count days on the ordinary Gregorian calendar, and the Julian Day is just a running day count. Because the names overlap, the terms ordinal date or day of year are clearer.

What does the code 27045 mean?

Day 45 of 2027, which is Sunday 14 February 2027. The first two digits are the year and the last three the day of the year. 2027045 is the same date written with a four-digit year.

What is the Julian date for 1 March?

Day 060 in a normal year such as 2027 (27060), and day 061 in a leap year such as 2028 (28061), because 29 February comes first.

How many days are in 2027?

365. 2027 is not a leap year, so 31 December 2027 is day 365 (27365). 2028 is a leap year with 366 days.

What is the Julian Day number for 1 January 2027?

JD 2461406.5 at midnight UT (the Julian Day starts at noon, so midnight is a half day). The MJD is 61406.

What is JD 2451545.0?

Noon on 1 January 2000, the J2000.0 epoch used in astronomy. Strictly that epoch is defined in Terrestrial Time, about a minute ahead of UTC; this converter works in UT and does not add leap seconds.

What is the Modified Julian Date?

MJD = JD − 2400000.5. It starts at midnight on 17 November 1858, so its days begin at midnight instead of noon and the numbers are shorter.

What about dates before 1582?

For the Julian Day, dates up to 4 October 1582 are read on the Julian calendar and dates from 15 October 1582 on the Gregorian calendar, as the US Naval Observatory does; 5 to 14 October 1582 do not exist. Day-of-year codes are worked out on the Gregorian calendar from 1583. The converter covers the years 1 to 9999.

Is my information uploaded?

No. Everything is worked out in this browser, and the files you download are made on your device.