One week after Election Day, control of the U.S. House rests on just over a dozen races where winners have not yet been determined.

Nine states have at least one uncalled House race, some of which are so close they are headed to a recount.

Then there’s California. About half of the yet-to-be-decided House races are in the state, which has only counted about three-quarters of its votes statewide.

This isn’t unusual or unexpected, as the nation’s most populous state is consistently among the slowest to report all its election results. Compare it to a state like Florida, the third-largest, which finished counting its votes four days after Election Day.

The same was true four years ago, when Florida reported the results of nearly 99% of ballots cast within a few hours of polls closing. In California, almost one-third of ballots were uncounted after election night, and the state was making almost daily updates to its count through Dec. 3, a full month after Election Day.

These differences in how states count — and how long it takes — exist because the Constitution sets out broad principles for electing a national government, but leaves the details to the states. The choices made by state lawmakers and election officials as they sort out those details affect everything from how voters cast a ballot to how quickly the tabulation and release of results takes place, how elections are kept secure and how officials maintain voters’ confidence in the process.

The gap between when California and Florida are able to finalize their count is the natural result of election officials in the two states choosing to emphasize different concerns and set different priorities. Heres a look at the differences:

How California counts

Lawmakers in California designed their elections to improve accessibility and increase turnout. Whether it’s automatically receiving a ballot at home, having up until Election Day to turn it in or having several days to address any problems that may arise with their ballot, Californians have a lot of time and opportunity to vote. It comes at the expense of knowing the final vote counts soon after polls close.

“Our priority is trying to maximize participation of actively registered voters,” said Democratic Assemblymember Marc Berman, who authored the 2021 bill that permanently switched the state to all-mail elections. “What that means is things are a little slower. But in a society that wants immediate gratification, I think our democracy is worth taking a little time to get it right and to create a system where everyone can participate.”

California, which has long had a culture of voting absentee, started moving toward all-mail elections last decade. All-mail systems will almost always prolong the count. Mail ballots require additional verification steps — each must be opened individually, validated and processed — so they can take longer to tabulate than ballots cast in person that are then fed into a scanner at a neighborhood polling place.

In 2016, California passed a bill allowing counties to opt in to all-mail elections before instituting it statewide on a temporary basis in 2020 and enshrining it in law in time for the 2022 elections.

Studies found that the earliest states to institute all-mail elections – Oregon and Washington – saw higher turnout. Mail ballots also increase the likelihood of a voter casting a complete ballot, according to Melissa Michelson, a political scientist and dean at California’s Menlo College who has written on voter mobilization.

In recent years, the thousands of California voters who drop off their mail ballots on Election Day created a bottleneck on election night. In the past five general elections, California has tabulated an average of 38% of its vote after Election Day. Two years ago, in the 2022 midterm elections, half the state’s votes were counted after Election Day.

Slower counts have come alongside later mail ballot deadlines. In 2015, California implemented its first postmark deadline, meaning that the state can count mail ballots that arrive after Election Day as long as the Postal Service receives the ballot by Election Day. Berman said the postmark deadline allows the state to treat the mailbox as a drop box in order to avoid punishing voters who cast their ballots properly but are affected by postal delays.

Initially, the law said ballots that arrived within three days of the election would be considered cast in time. This year, ballots may arrive up to a week after Election Day, so California won’t know how many ballots have been cast until Nov. 12. This deadline means that California will be counting ballots at least through that week because ballots arriving up to that point might still be valid and be added to the count.

How Florida counts

Florida’s election system is geared toward quick and efficient tabulation. Coming out of its disastrous 2000 presidential election, when the U.S. Supreme Court settled a recount dispute and George W. Bush was declared the winner in the state over Al Gore, the state moved to standardize its election systems and clean up its canvass, or the process of confirming votes cast and counted.

Republican Rep. Bill Posey, who as state senator was the sponsor of the Florida Election Reform Act of 2001, said the two goals of the law — to count all legal votes and to ensure voters are confident their votes are counted — were accomplished by mandating optical ballot scanners in every precinct. That “most significant” change means no more “hanging chads” in Florida. The scanners read and aggregate results from paper ballots, immediately spitting back any that contain mistakes.

Florida’s deadlines are set to avoid having ballots arrive any later than when officials press “go” on the tabulator machines. The state has a receipt deadline for its absentee ballots, which means ballots that do not arrive by 7 p.m. local time on Election Day are not counted, regardless of when they were mailed.

Michael T. Morley, a professor of election law at Florida State University College of Law, pointed out that Florida election officials may begin processing ballots, but not actually count them, before polls close. That helps speed up the process, especially compared with states that don’t allow officials to process mail ballots before Election Day.

“They can determine the validity of ballots, confirm they should be counted and run them through machines,” Morley said. “They just can’t press the tally button.”

Florida takes steps to avoid a protracted back-and-forth on potentially problematic ballots. At the precinct, optical scanners catch some problems, such as a voter selecting too many candidates, that can be fixed on-site. Also, any voter who’s returned a mail ballot with a mismatched or missing signature has until 5 p.m. two days after the election to submit an affidavit fixing it. California gives voters up to four weeks after the election to address such inconsistencies.

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Read more about how U.S. elections work at Explaining Election 2024, a series from The Associated Press aimed at helping make sense of the American democracy. The AP receives support from several private foundations to enhance its explanatory coverage of elections and democracy. See more about AP’s democracy initiative here. The AP is solely responsible for all content.