What fraction of the Senate is elected every two years?

Each term for a United States Senator is six years long, and the Senate is structured so that approximately one-third of its members are elected every two years. This staggered election cycle ensures that the Senate maintains continuity while allowing for regular opportunities for voters to elect new representatives. Since there are 100 Senators in total, this means that roughly 33 out of 100 are up for election during each election cycle, which can be described as one-third.

This system contrasts with the House of Representatives, where every member is elected every two years. The staggered election of Senators is intended to create stability within the Senate as it makes it less likely that both chambers will turn over completely during a single election, thereby fostering a degree of institutional knowledge and experience among its members.