The number of special elections to each meeting of Congress has steadily increased over the past twenty years, from an average of 7.6 special elections in the five meetings beginning in 1993, to 11.6 in the five meetings starting in 2003, and to 13.4 in the five meetings that began in 2013 and ended in 2022.
| Meeting of Congress | Years | Average number of all special special elections per meeting | Average number of U.S. House special elections per meeting |
| 113-117 | 2013-2021 | 13.4 | 11 |
| 108-112 | 2003-2012 | 11.6 | 10.2 |
| 103-107 | 1993-2002 | 7.6 | 6.2 |
A meeting of Congress spans the period of time between two-year election cycles for the full U.S. House and one-third of the U.S. Senate. Each meeting of Congress typically has two sessions, one in each calendar year, as the Constitution requires that Congress meet annually.
The trend of more special elections to Congress in recent years held for both the U.S. House and Senate. The average number of House special elections per meeting increased from 6.2 in the earliest period analyzed to 11 in the most recent. The average number of Senate special elections per meeting increased from 1.4 in the earliest period analyzed to 2.4 in the most recent.
Special elections to Congress occur when a legislator resigns or is removed from office. The Constitution requires that vacancies in the House be filled through an election. The process for filling House vacancies is distinct from filling vacancies in the U.S. Senate, where 37 states fill vacancies through gubernatorial appointment, and the remaining 13 require a special election.
Depending on the specific state laws governing vacancies, a state can either hold an election within the same calendar year or wait until the next regularly scheduled election.
See the table below for the number of special elections by meeting of Congress from 1993 through the end of 2022, or the 103rd meeting of the U.S. Congress to the 117th.
| Meeting of Congress | Years | Total special elections | U.S. House elections | U.S. Senate elections |
| 117 | 2021-2022 | 17 | 15 | 2 |
| 116 | 2019-2020 | 10 | 8 | 2 |
| 115 | 2017-2018 | 17 | 14 | 3 |
| 114 | 2015-2016 | 7 | 7 | 0 |
| 113 | 2013-2014 | 16 | 11 | 5 |
| 112 | 2011-2012 | 11 | 11 | 0 |
| 111 | 2009-2010 | 15 | 10 | 5 |
| 110 | 2007-2008 | 14 | 12 | 2 |
| 109 | 2005-2006 | 12 | 12 | 0 |
| 108 | 2003-2004 | 6 | 6 | 0 |
| 107 | 2001-2002 | 6 | 5 | 1 |
| 106 | 1999-2000 | 9 | 8 | 1 |
| 105 | 1997-1998 | 3 | 3 | 0 |
| 104 | 1995-1996 | 11 | 9 | 2 |
| 103 | 1993-1994 | 9 | 6 | 3 |
