The Senate divides its seats into three classes so that regular elections renew roughly one-third of the chamber every two years. Senators serve six-year terms.
This creates continuity: many senators remain in office while other seats are contested.
Which class is associated with 2026?
Class II terms in the current cycle end on January 3, 2027. The Senate's official class page explains the timing and lists the seats in that group. Source: Senate Class II page.
The class identifies the seat's regular election schedule. It does not guarantee that the same officeholder seeks reelection or becomes the nominee.
Two senators, different cycles
A state's two senators belong to different classes. Voters therefore do not ordinarily choose both in the same regular cycle.
A ballot can nevertheless contain a special Senate election in addition to the regular schedule. Special elections address vacancies and the remaining term rather than changing the basic three-class system.
Check the office and term description on the ballot.
Why the map affects political analysis
A party's opportunity to gain seats depends on which states are voting, not just on national opinion. A national shift has different possible consequences under different Senate maps.
Imagine a party enjoying improved national support while many of the seats it could contest are in states strongly favorable to its opponents. That environment is different from a cycle with more closely divided states.
The example illustrates why national polling cannot be converted directly into a Senate seat forecast.
Held seats and contested seats are different totals
A Senate-control tracker must include seats that are not regularly contested as well as outcomes of the relevant elections.
A chart showing only the election-night winners can be useful, but it must not be mistaken for the full chamber division.
How to verify a claim
Use the Senate class list for the regular cycle and current state notices for special elections. Check whether the article refers to a candidate, an incumbent, an appointed senator, or a particular seat.
That precision prevents errors such as describing every current senator as a candidate in November.
Related reading: special Senate elections and tracking Senate control.