Convert between the Julian and Gregorian calendars
The Julian calendar was used across Europe until the Gregorian reform of 1582, which corrected an accumulating drift by removing ten days and tightening the leap-year rule. As a result, historical dates recorded in the Julian system sit several days apart from the modern Gregorian calendar — a gap that grows over the centuries.
How it works
The converter routes both calendars through the Julian Day Number (JDN), a continuous count of days that is independent of any calendar:
- The input date is converted to its JDN using that calendar’s leap-year rule.
- The JDN is converted back into the other calendar’s year, month and day.
Because every conversion passes through the same day count, the two directions are exact inverses, and the JDN is shown so you can verify the offset yourself. The difference between the calendars depends on the century:
| Gregorian period | Julian is behind by |
|---|---|
| 1500–1699 | 10 days |
| 1700–1799 | 11 days |
| 1800–1899 | 12 days |
| 1900–2099 | 13 days |
Example
The Gregorian date 14 March 1879 corresponds to the Julian date 2 March 1879 — a 12-day gap for the 19th century. Convert the other way and 2 March 1879 (Julian) returns 14 March 1879 (Gregorian), with the same Julian Day Number on both sides.
Pick a direction, enter the year, month and day, and the equivalent date appears instantly — all in your browser, nothing uploaded.