📆 Julian Date Converter
Convert dates to Julian dates both ways: the YYDDD day-of-year code used on packaging and by the military, and the astronomical Julian Date (JD and MJD).
Day of year on the 1st of each month
| Month | Common year | Leap year |
|---|---|---|
| January 1 | 001 | 001 |
| February 1 | 032 | 032 |
| March 1 | 060 | 061 |
| April 1 | 091 | 092 |
| May 1 | 121 | 122 |
| June 1 | 152 | 153 |
| July 1 | 182 | 183 |
| August 1 | 213 | 214 |
| September 1 | 244 | 245 |
| October 1 | 274 | 275 |
| November 1 | 305 | 306 |
| December 1 | 335 | 336 |
What Julian Date Converter Does
“Julian date” means two different things, and this converter handles both. On food packaging, in manufacturing, and in military and government records, it usually means an ordinal date: the year followed by the day of the year, such as 26267 or 2026267 for September 24, 2026. In astronomy it means the Julian Date (JD), a continuous count of days since noon UTC on January 1, 4713 BC — 2461308.0 for noon on the same day.
Today’s value in each form appears as soon as the page loads. Pick any date to convert it, or type a code or a JD to convert it back to a calendar date — including the short one-digit year codes stamped on egg cartons and lot numbers. The astronomical mode also gives the Modified Julian Date and accepts a time of day in UTC.
How to Use Julian Date Converter
- Choose the day-of-year (YYDDD) form or the astronomical Julian Date
- Pick a calendar date — today is filled in automatically
- Read the Julian date, or the JD and MJD with a time in UTC
- Type a code like 26267 or a JD to convert it back to a date
- Use the month table to find day numbers by hand
Formula Used by Julian Date Converter
Ordinal (YYDDD) date
Julian date = last two digits of the year + day of year (001–366)
Worked example
September 24, 2026.
- 243 days before September (31+28+31+30+31+30+31+31)
- 243 + 24 = day 267
Result: 26267, or 2026267 with a four-digit year.
Astronomical Julian Date
JD = ⌊365.25(Y + 4716)⌋ + ⌊30.6001(M + 1)⌋ + D + B − 1524.5 (Meeus), with January and February counted as months 13 and 14 of the previous year
Worked example
January 1, 2000, 12:00 UTC.
- Y = 1999, M = 13, B = −13
- Evaluate the terms
Result: JD 2451545.0 (the J2000.0 epoch); MJD 51544.5.
Reference Epochs
| Date (UTC) | Julian Date | Modified Julian Date |
|---|---|---|
| Nov 17, 1858, 00:00 | 2400000.5 | 0 |
| Jan 1, 1970, 00:00 (Unix epoch) | 2440587.5 | 40587 |
| Jan 1, 2000, 12:00 (J2000.0) | 2451545.0 | 51544.5 |
| Jan 1, 2026, 00:00 | 2461041.5 | 61041 |
How to Read Your Result
Reading food codes
An ordinal code usually marks when a product was made or packed, not when it expires. Egg cartons in the U.S., for example, often show the pack date as a three-digit day of the year, with the sell-by or best-by date printed separately. Manufacturers use their own formats, so the letters and digits around the date vary.
Why astronomers count days
A single running day count makes it easy to find the time between two observations — just subtract — without worrying about months, leap years or calendar reforms. Starting days at noon kept a whole night’s observations under one date for European astronomers.
Limitations & Accuracy Notes
- Astronomical conversions are for dates from October 15, 1582 (the Gregorian calendar) onward.
- Two-digit year codes are read with the usual pivot: 00–68 as 2000–2068, 69–99 as 1969–1999.
- Times are in UTC; convert local time before entering.