1784 (MDCCLXXXIV) was a leap year starting on Thursday of the Gregorian calendar and a leap year starting on Monday of the Julian calendar, the 1784th year of the Common Era (CE) and Anno Domini (AD) designations, the 784th year of the 2nd millennium, the 84th year of the 18th century, and the 5th year of the 1780s decade. As of the start of 1784, the Gregorian calendar was 11 days ahead of the Julian calendar, which remained in localized use until 1923.