A seat in Congress can open up in the middle of a term. When it does, the district or state keeps its seat in the chamber, but it has no one casting votes until the seat is filled. How it gets filled depends entirely on which chamber it is.
How seats become vacant
Vacancies happen for a handful of reasons. A member dies in office. A member resigns, sometimes to take another job, sometimes under pressure. A member is expelled by their chamber, which is rare. A member-elect declines to take the seat. Occasionally a seat is vacant at the start of a Congress because an election was not resolved in time.
House seats must be filled by election
The Constitution is strict about the House. Article I, Section 2 says that when a vacancy happens, the executive authority of the state shall issue writs of election to fill it. There is no appointment power. A House seat can only be filled by the voters, through a special election.
That means a House vacancy can last a long time. The governor sets the date within whatever window state law allows, and the process often takes several months. During that time the district has no representative casting floor votes, though the office usually stays open and staff continue helping constituents with casework.
Senate seats are usually filled by appointment first
The Senate works differently. The Seventeenth Amendment lets a state legislature authorize its governor to appoint someone to serve until a special election is held. Most states have done exactly that, so a Senate vacancy is typically filled within days or weeks. A few states require an election and do not allow an appointment.
The appointed senator has the same voting power as an elected one. See how U.S. senators are appointed to fill vacancies for how that process works and how long appointees serve.
What a vacancy changes
A vacancy lowers the number of votes needed to pass something in that chamber, because thresholds are usually based on members present and voting. In a closely divided House, one or two vacancies can matter on a given bill. It also leaves a district without a vote on legislation, which is why states are generally quick to schedule replacements.
Vacancies do not change the total size of the chamber. The House still has 435 seats and the Senate still has 100, whether or not every seat is occupied.
How this site shows vacant seats
When a House district has no sitting representative, its page on this site is marked vacant and explains who last held the seat and what is scheduled next. You can see which districts are currently vacant on the Browse Districts page by using the Vacant filter.
Related reading
For the terms used here, see the glossary. For the current cycle, see the 2026 Congressional Elections Tracker and the 2026 Senate elections tracker. To find your own district, use the lookup on the home page.
Vacancy status on this site is checked against primary government records. See how we source our data and our editorial standards.
Last updated September 3, 2026.
