1810 (MDCCCX) was a common year starting on Monday of the Gregorian calendar and a common year starting on Saturday of the Julian calendar, the 1810th year of the Common Era (CE) and Anno Domini (AD) designations, the 810th year of the 2nd millennium, the 10th year of the 19th century, and the 1st year of the 1810s decade. As of the start of 1810, the Gregorian calendar was 12 days ahead of the Julian calendar, which remained in localized use until 1923.