Julian Date Converter
Convert any date to its Julian date and back, in both senses: the ordinal day-of-year stamp such as 26245, and the astronomical Julian Day Number. Both are on the page at once for the same date, each converting in either direction, with today's values ready when the page opens. The day of the year, the five-digit and seven-digit ordinal forms, the Julian Day Number, the Julian Date at midnight UTC, the Modified Julian Date and the weekday are all listed, and a table below gives the ordinal number of the first and last day of every month in a common year and a leap year.
Julian dateLoading today's date.
Two different numbers share one name. The ordinal date is the day of the year with a two-digit year in front, 001 to 365 or 366, which is what a packaging stamp, a ration date or a mainframe date field means by "Julian". The Julian Day Number is the astronomers' running count of days since noon UTC on 1 January 4713 BC, seven digits long today, with the Julian Date adding the fraction of the day from noon and the Modified Julian Date subtracting 2400000.5 to start the day at midnight. Both are shown for every date so nobody has to guess which one was meant. Dates run from year 1 to 9999, which is Julian Day Number 1721426 to 5373484. Leap years follow the Gregorian rule throughout, including for dates before 1582.
Ordinal day numbers by month
The ordinal number of the first day of each month in a common year and in a leap year, and of the last day of each. Everything from 1 March on is one higher in a leap year. Computed by the same code as the converter rather than typed in.
| Month | 1st, common year | 1st, leap year | Last day, common year | Last day, leap year |
|---|---|---|---|---|
| January | 001 | 001 | 031 | 031 |
| February | 032 | 032 | 059 | 060 |
| March | 060 | 061 | 090 | 091 |
| April | 091 | 092 | 120 | 121 |
| May | 121 | 122 | 151 | 152 |
| June | 152 | 153 | 181 | 182 |
| July | 182 | 183 | 212 | 213 |
| August | 213 | 214 | 243 | 244 |
| September | 244 | 245 | 273 | 274 |
| October | 274 | 275 | 304 | 305 |
| November | 305 | 306 | 334 | 335 |
| December | 335 | 336 | 365 | 366 |
Common questions
- Which Julian date do I need, the ordinal date or the Julian Day Number?
- If the number is on packaging, a ration, a medical supply, a military document or a mainframe date field, it is the ordinal date: the day of the year, usually with a two-digit year in front, so 26245 is day 245 of 2026, which is 2 September. If the number is seven digits starting 24 or 25 and comes from astronomy, satellite tracking, a telescope log or a scientific data set, it is the Julian Day Number, the count of days since noon UTC on 1 January 4713 BC, so 2451545 is 1 January 2000. Both are shown here for the same date, and the Mode control picks which one you have.
- How do I read a code like 26245?
- The first two digits are the year and the last three are the day of the year: 26245 is day 245 of 2026, which is 2 September. Day 001 is 1 January, and the table on this page gives the first and last day number of each month, so 245 lands in September because September runs from 244 to 273 in a common year. Some codes drop the year and print only the three-digit day; type that on its own and the converter places it in the current year. A seven-digit code such as 2026245 is the same thing with the full year, which is how ISO 8601 writes an ordinal date.
- What year does a two-digit year like 26 mean?
- 2026. A five-digit stamp is read as 2000 to 2099, because that is what every code on a shelf or in a current file means. For a date in another century type all four digits of the year, as 1999365 or 1999-365, and it is read as written. Dates from year 1 to year 9999 are accepted.
- How do leap years change the ordinal date?
- Every date from 1 March onwards is one day later in a leap year, because 29 February takes day 060. So 1 March is day 060 in a common year and 061 in a leap year, and 31 December is day 365 or 366. Leap years follow the Gregorian rule, every fourth year except century years unless divisible by 400: 2024 and 2000 are leap years, 2100 is not. The converter refuses day 366 in a common year and says how many days that year has. The reference table shows both columns side by side.
- What is the Julian Day Number, and why does the Julian Date start at noon?
- The Julian Day Number is a running count of days with no months or years in the way, so the gap between two dates is one subtraction. Day 0 was 1 January 4713 BC in the old Julian calendar, chosen by Joseph Scaliger in 1583, and the count has never been reset: 1 January 2000 was JDN 2451545 and 2 September 2026 is 2461286. The Julian Date adds a fraction of the day, and that fraction is counted from noon UTC, because astronomers wanted a whole night's observing to fall on one number. So midnight UTC opening 1 January 2000 is JD 2451544.5, and if you type a Julian Date with a fraction the converter rounds it to the day it falls in and says so.
- What is the Modified Julian Date?
- The Julian Date minus 2400000.5. The half day moves the start of the day to midnight, and the 2400000 drops two digits, so a date this century is a five-digit number: 1 January 2000 is MJD 51544 and 2 September 2026 is MJD 61285. MJD 0 is 17 November 1858. It is used in satellite tracking, space telemetry and time-signal work. Pick MJD next to the field in JDN mode to type one directly, or read it from the list for any date.
- What is today's Julian date?
- The page opens on today, read from your device's own calendar, so the two large numbers at the top are today's ordinal stamp and today's Julian Day Number. The Today button brings any other date back to it. The date is read from your calendar rather than the UTC instant, so it is the day on your wall rather than the day in Greenwich, which is already tomorrow for part of the world every evening.
Exact. The ordinal date counts days from 1 January, and the Julian Day Number uses the standard Gregorian algorithm; both are checked against known dates in the tests.