Primary election definition
In primary elections, voters help choose party nominees who will compete in the general election for federal offices.
A primary election decides which candidates a political party sends to the general election. Voters usually vote in the primary of the party they’re registered with. Federal primaries are held for the offices of president, US senator, and US representative.
For congressional candidates, the primary winner becomes the party's nominee, while presidential nominees are chosen later at each party's national convention.
Most primaries are run by state and local election officials. Parties are not required to hold one, and can instead choose to pick nominees with a caucus, a meeting run by the party.
How do primary elections work?
In a primary election, voters cast a secret ballot for one candidate from a single party. Typically, the candidate with the most votes wins the nomination. Some states require a majority, or more than half the votes; if no candidate reaches it, the top two meet again in a primary runoff election.
Presidential primaries work differently. Voters don’t select a candidate directly, but pick delegates who represent their state at the party's national convention. The convention delegates then select the nominee.
Who can vote in a primary election?
Primary election rules depend on the state. As of December 2025, 44% of states held an open primary or one open to unaffiliated voters. In an open primary, any registered voter can take part regardless of their party affiliation.
Closed primaries happen in 20% of states and Washington, DC. In a closed primary, only voters registered with the party holding the primary may vote.
Another 26% of states fall somewhere in between. States with partially closed primaries let each state party decide whether unaffiliated voters may participate. Those with partially open primaries let voters choose any party's ballot, but they must say which one they are taking. In some states that choice may also change their party registration.
The remaining 10% of states use other formats. In a top-two or top-four primary, all candidates appear on one ballot. The two or four with the most votes advance to the general election, even if they share a party. Louisiana runs its House races differently. All candidates appear on one ballot, and a candidate who wins a majority is elected outright, with no general election.
When are primary elections held?
Primary election dates are set by state law and are spread throughout the year. Congressional primaries in 2026 run from March 3 in Arkansas, North Carolina, and Texas through September 15 in Delaware.
Presidential primaries and caucuses are held from January to June in presidential election years. The nominating conventions happen from July to early September.
Keep exploring
- In today's Congress, three seats can decide everything. - Unlike the large majorities of the past, today’s congressional control often hinges on only a few seats changing hands.
- Reapportionment and redistricting after the 2020 census: Explained - Texas gained two congressional seats while seven states lost a seat following the 2020 census. In all, seven seats shifted between 13 states.
- House members have all but stopped crossing party lines. - USAFacts reviewed more than 30 years of House roll call votes to measure how often members cross party lines.
- More voters are registering outside the two party system - We mapped voter registration in every state that tracks party affiliation. In three out of four counties, the share of voters registered outside the two major parties grew over the past decade.
