In a closed primary, only voters registered with a party can vote in that party’s primary. In an open primary, any registered voter can choose either party’s ballot on primary day, regardless of registration. Most states sit somewhere in between, and a few have dropped party primaries altogether in favor of one ballot for all candidates. The rules decide who picks the nominees, which is often who effectively picks the winner.
What is a closed primary? #
Only voters registered as party members can vote in that party’s primary. Registered Democrats get the Democratic ballot, registered Republicans get the Republican ballot, and unaffiliated voters generally can’t vote for party nominees at all, though they can still vote on any nonpartisan races or ballot measures held the same day.
Switching parties to vote in a different primary usually has to happen by a deadline, sometimes weeks or months ahead. New York, Pennsylvania, Florida, Delaware, Kentucky and Maryland are among the states known for closed primaries.
Supporters say parties are private associations whose members should choose their standard-bearers, and closed primaries prevent opponents from crossing over to meddle.
Critics say closed primaries shut out a large and growing share of voters who don’t join a party, while their taxes pay for the election.
What is an open primary? #
Any registered voter can choose which party’s ballot to take, privately, on primary day. You can vote in only one party’s primary per election, but you don’t have to register with that party. Michigan, Minnesota, Wisconsin, Vermont and Montana are among the states with open primaries.
Supporters say open primaries include independents and give nominees an incentive to appeal beyond the party base.
Critics say they let voters from the other party “raid” a primary to pick a weak nominee. Coordinated raiding is rare in practice, but crossover voting does happen in lopsided states where one party’s primary is the only competitive contest.
What are semi-closed and semi-open primaries? #
Most states use a hybrid.
| Type | Party members | Unaffiliated voters | Other party’s members |
|---|---|---|---|
| Closed | Own party only | Can’t vote for party nominees | No |
| Semi-closed (open to unaffiliated) | Own party only | Can choose one party’s ballot | No |
| Semi-open (partially open) | Any party’s ballot | Any party’s ballot | Any, but the choice is public or recorded |
| Open | Any party’s ballot | Any party’s ballot | Any, choice kept private |
In semi-closed states such as Arizona, Colorado, Massachusetts, New Hampshire and North Carolina, independents can pick a party’s ballot while registered partisans stay in their lane. In semi-open states, anyone can vote in either primary, but requesting a party’s ballot is recorded, and in some states it counts as affiliating with that party. Our explainer on semi-closed primaries goes into the details.
Parties can also set their own rules within state law, so a state’s Republican and Democratic primaries don’t always work the same way.
What are top-two and top-four primaries? #
Some states have replaced party primaries with a single ballot listing every candidate from every party.
- Top-two (California, Washington): everyone runs on one primary ballot, and the two highest vote-getters advance to November regardless of party. Two Democrats or two Republicans sometimes face off in the general.
- Top-four (Alaska): the top four advance, and the general election uses ranked-choice voting. Alaska voters narrowly rejected a repeal in 2024, and another repeal measure is on the ballot on November 3, 2026.
- Louisiana: long known for its all-candidate “jungle” system, Louisiana passed a law to hold closed party primaries for Congress starting in 2026. After the Supreme Court’s Louisiana v. Callais ruling in April 2026, the state postponed its spring primary and redrew its map, and its 2026 House races are being decided on an all-candidate ballot on November 3, with a December 12 runoff if no one tops 50%.
Our guide to jungle primaries covers how these systems play out. Reform efforts continue in other states. Nevada voters approved open top-five primaries with ranked-choice general elections in 2022, but the measure failed the required second vote in 2024.
How do primary rules affect nominees? #
The common argument is that closed primaries produce more ideological nominees and open or top-two systems produce more moderate ones. The evidence is mixed. Studies of California’s top-two system found smaller moderating effects than its backers hoped, largely because primary voters in every system tend to be older, more partisan and more engaged than general-election voters.
Turnout effects are clearer: primaries that let independents participate usually draw more voters than closed ones. And rules matter most in safe seats, where the dominant party’s primary is effectively the election. In those districts, who’s allowed to vote in the primary decides who represents everyone.
Why primary rules make polling harder #
Primary polls are among the least reliable polls anyone publishes, and the rules are part of the reason.
- Closed primaries have small, partisan electorates, and small shifts in turnout among committed factions can swing results.
- Open primaries are hard to screen, because the pollster has to guess which independents and crossover voters will take which ballot.
- Top-two and top-four primaries have many candidates from both parties on one ballot, so the poll has to measure a crowded field rather than a head-to-head.
For the 2028 presidential primaries, Election Tracker, our free iPhone app, shows polls for both parties’ fields on its 2028 Primary tab. Each field gets its own 30-day average and trend line, and every poll lists its sample and population, so you can see whether a pollster surveyed a party’s registered members, its likely primary voters, or everyone who leans that way.
Frequently asked questions #
Can I vote in both the Democratic and Republican primaries? #
No. In every system you can vote in only one party’s primary for a given election. In top-two and top-four states there’s a single ballot, so the question doesn’t arise.
Can independents vote in primaries? #
It depends on the state. In open, semi-open and semi-closed states, independents can choose a party ballot. In closed states they can’t vote for party nominees unless they register with a party by the deadline. In top-two and top-four states, everyone gets the same ballot.
How do I find my state’s primary rules? #
Your state election office’s website explains who can vote in each party’s primary and the deadline for changing party registration. Rules change, and parties sometimes set their own, so check before each election.
Which is more common, open or closed primaries? #
Pure open and pure closed systems are each a minority; most states use a hybrid of some kind. How states are counted varies by source, because parties within the same state can use different rules.
Do open primaries produce more moderate candidates? #
Sometimes, but less than often claimed. Research finds modest effects at best, because the people who vote in primaries tend to be the most engaged partisans under any system.