When must Congress meet at least once a year?

Congress is required to meet at least once a year on January 3rd, as stipulated by the 20th Amendment to the Constitution. This amendment, ratified in 1933, established this date as the beginning of each new Congress. It serves to ensure that Congressional meetings are timely and that legislative business can be addressed promptly after elections. January 3rd is specifically chosen to ensure that there is a consistent schedule for starting each new session of Congress, reflecting the need for regular legislative operations in the federal government.