1812 (MDCCCXII) was a leap year starting on Wednesday of the Gregorian calendar and a leap year starting on Monday of the Julian calendar, the 1812th year of the Common Era (CE) and Anno Domini (AD) designations, the 812th year of the 2nd millennium, the 12th year of the 19th century, and the 3rd year of the 1810s decade. As of the start of 1812, the Gregorian calendar was 12 days ahead of the Julian calendar, which remained in localized use until 1923.