According to the Congressional Research Service, the average length of service for members of the House of Representatives and the Senate has varied substantially since 1789. As of the beginning of the 118th Congress, which convened on January 3, 2023, the average length of service for Representatives was 8.5 years (4.3 House terms), while for Senators it was 11.2 years.

The average years of service of Members in both chambers has generally increased over time. For example, the average House service reached an all-time high of 10.2 years during the 102nd Congress (1991-1993) . The prior House service of incoming Representatives increased from an average of 2.5 years in the 19th century to 9.4 in the 21st century to date.

It is worth noting that the percentage of Members choosing to seek reelection and the success rate of Members who do seek reelection are factors that affect the average years of service. Additionally, roughly 24% of the current Congress has twelve years or more experience in at least one chamber, and the trend is on the rise.