1612 (MDCXII) was a leap year starting on Sunday of the Gregorian calendar and a leap year starting on Wednesday of the Julian calendar, the 1612th year of the Common Era (CE) and Anno Domini (AD) designations, the 612th year of the 2nd millennium, the 12th year of the 17th century, and the 3rd year of the 1610s decade. As of the start of 1612, the Gregorian calendar was 10 days ahead of the Julian calendar, which remained in localized use until 1923.