1817 (MDCCCXVII) was a common year starting on Wednesday of the Gregorian calendar and a common year starting on Monday of the Julian calendar, the 1817th year of the Common Era (CE) and Anno Domini (AD) designations, the 817th year of the 2nd millennium, the 17th year of the 19th century, and the 8th year of the 1810s decade. As of the start of 1817, the Gregorian calendar was 12 days ahead of the Julian calendar, which remained in localized use until 1923.