1648 (MDCXLVIII) was a leap year starting on Wednesday of the Gregorian calendar and a leap year starting on Saturday of the Julian calendar, the 1648th year of the Common Era (CE) and Anno Domini (AD) designations, the 648th year of the 2nd millennium, the 48th year of the 17th century, and the 9th year of the 1640s decade. As of the start of 1648, the Gregorian calendar was 10 days ahead of the Julian calendar, which remained in localized use until 1923.