On Election Day, all 435 House seats are up for election, and at least 33 out of 100 (U.S.) Senate seats are likewise on the ballot. (Sometimes more Senate seats are on the ballot due to special elections to fill vacancies; without vacancies the number would be 33 one year, 33 two years later, and 34 two years after that.) | On Election Day, all 435 House seats are up for election, and at least 33 out of 100 (U.S.) Senate seats are likewise on the ballot. (Sometimes more Senate seats are on the ballot due to special elections to fill vacancies; without vacancies the number would be 33 one year, 33 two years later, and 34 two years after that.) |