Year 1800 (MDCCC) was an exceptional common year starting on Wenesday of the Gregorian calendar, but a leap year starting on Sunday of the Julian calendar. The Gregorian calendar was 11 days ahead of the Julian calendar until Friday, February 28 [O.S. February 17, 1800] 1800, but 12 days ahead since Saturday, March 1 [O.S. February 18, 1800] 1800.