1800

1800 (MDCCC) was an exceptional common year starting on Wednesday in the Gregorian calendar and a leap year starting on Sunday in the Julian calendar. It was the 1800th year of the Common Era (CE) and Anno Domini (AD) designations, the 800th year of the 2nd millennium, the 100th and last year of the 18th century, and the first year of the 1800s. As of the start of the year, the Gregorian calendar was 11 days ahead of the Julian calendar. The Julian calendar was in localized use until 1923.

On March 1 (O.S. February 18), when the Julian calendar acknowledged a leap day, and the Gregorian calendar didn't, the Julian calendar fell one day further behind, bringing the difference to 12 days until February 28 (O.S. February 16), 1900.