As of January 13, 2020, 2,271 major party candidates have filed to run for the Senate and House of Representatives in 2020.

So far, 329 candidates are filed with the Federal Elections Commission (FEC) to run for U.S. Senate. Of those, 281—148 Democrats and 133 Republicans—are from one of the two major political parties. In 2018, 527 candidates filed with the FEC to run for U.S. Senate, including 137 Democrats and 240 Republicans.

For U.S. House, 2,165 candidates are filed with the FEC to run in 2020. Of those, 1,990—974 Democrats and 1,016 Republicans—are from one of the two major political parties. In 2018, 3,244 candidates filed with the FEC, including 1,566 Democrats and 1,155 Republicans.

While no new congressional retirements were announced last week, Republican Rep. Duncan Hunter (CA-50) announced his resignation effective Jan. 13, and Gov. Gavin Newsom (D) announced he would not call a special election to fill the seat. This brings the total of open-seat congressional elections to 36.

Not including those who left office early, four senators (three Republicans and one Democrat) and 35 representatives (26 Republicans and nine Democrats) are not running for re-election. In 2018, 55 total members of Congress—18 Democrats and 37 Republicans—did not seek re-election.

On November 3, 2020, 35 Senate seats and all 435 House seats are up for election. Of those Senate seats, 33 are regularly scheduled elections, while the other two are special elections in Arizona and Georgia. Twelve are Democratic-held seats and 23 are Republican-held seats. In the House, where all seats are up for election, Democrats currently hold a majority with 232 seats.

Additional Reading:
United States House of Representatives elections, 2020
United States Senate elections, 2020
List of U.S. Congress incumbents who are not running for re-election in 2020