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.
This converter translates dates in either direction and shows the underlying Julian Day Number so you can verify the gap. Pick a direction, enter the year, month and day, and the equivalent date appears instantly — all in your browser.