The Twentieth Amendment (Amendment XX) to the United States Constitution moved the beginning and ending of the terms of the President and Vice President from March 4 to January 20, and of members of Congress from March 4 to January 3.
The Twentieth Amendment to the U.S. Constitution addresses the terms of elected Federal officials, including the President, Vice-President, and members of Congress. Specifically, it defines the actual dates on which those terms begin and end.