How to convert a Julian date
- Choose Date to Julian and pick a date, or Julian to date to go the other way.
- For Julian to date, pick the Format of the number you have and type it.
- Read the result in every format and click any value to copy it.
The formats side by side
For 12 October 2026:
| Format | Value | Used for |
|---|---|---|
| YYDDD | 26285 | Food and drug packaging, military dates, mainframe systems |
| YYYYDDD | 2026285 | The same with a four-digit year, so there’s no century mix-up |
| Ordinal date (ISO 8601) | 2026-285 | Standard day-of-year notation |
| Julian Day Number | 2461326 | Astronomy and software that counts days |
| Modified Julian Date | 61325 | Space science and satellite data |
Two-digit years in YYDDD are read as 2000 to 2069 for 00 to 69, and 1970 to 1999 for 70 to 99.
How the day number is counted
The day of the year counts 1 January as day 001, so 1 February is 032 and 31 December is 365, or 366 in a leap year. The table under the tool lists the first and last day number of each month for the year you chose, which is handy when you’re reading a batch of codes by hand. From March onwards every day number is one higher in leap years.