Current congressional retirement and party makeup data comes from the U.S. House of Representatives Press Gallery’s official casualty list and party breakdown page. Historical retirement data through the 113th Congress (2013-2015) was compiled from earlier versions of that webpage, accessed via the Internet Archive.

The Press Gallery distinguishes between members who are retiring and those who die in office or resign. Members who died in office and most members who resigned during their term are excluded. Representatives who announced their retirement but resigned in that term are classified as “resigned” and therefore excluded. This includes, for example, former representatives like Adam Schiff, D-Calif., and Kelly Armstrong, R-N.D., who retired to seek other offices and resigned several weeks before their final term officially ended. Five representatives are classified as “retiring” because they announced retirements during their final term but resigned three days before that term officially expired: Candice Miller, R-Mich., in the 114th; Michelle Lujan Grisham, D-N.M., in the 115th; Mike Doyle, D-Pa., and G.K. Butterfield, D-N.C., in the 117th; and Jeff Jackson, D-N.C., in the 118th.

Announcement dates were manually collected, based on news reports and official press releases. Representatives who announced plans to run for another office are recorded as running for that office even if they later withdrew from that race.

Reporting and research by Maya Sweedler, Eunice Esomonu and Leah Askarinam. Design and development by Maya Sweedler, Eunice Esomonu, Hyojin Yoo, Simran Parwani, and Pablo Barria Urenda. Editing by Ashlyn Still and Linda Gorman.