As votes are counted on Tuesday, many Americans will buckle in at home to watch the results of key races come in from across the country.

But it’s unlikely all races will be called on Tuesday night — and that’s normal.

Procedurally, it takes some time for ballots to be counted, especially the large share of mail-in and absentee ballots submitted this election cycle. Only races that can be determined with complete accuracy will be called on Tuesday night.

In the U.S., elections are run by state and local officials, all of which may have differing laws and rules around the ballot counting process.

Some states, for example, allow election officials to start counting ballots weeks before Election Day, while others do not authorize that process to occur until Election Day.

In Pennsylvania, where Democratic Senate nominee John Fetterman is running a tight race against GOP candidate Mehmet Oz, ballots cannot be readied to be tabulated until Election Day at 7 a.m. Unofficial returns in Pennsylvania must be reported to the secretary of commonwealth by 5 p.m. on Nov. 15.

In Arizona, another closely watched state this election cycle, ballots must be returned by 7 p.m. on Election Day, but officials have 20 days to finalize counts, according to The Associated Press.

The Associated Press is the only news organization that does all the math during elections and will call the roughly 7,000 races up and down the ballot.

The organization has more than 4,000 stringers on the ground in all 50 states for Election Day and about 60 people on an election team who will declare winners. It also has a dedicated fact-checking team.

The AP says Election Day is “not a one night affair,” explaining they do not make projections and only call races when it is clear that trailing candidates cannot close the gap.

“When the votes come in and they meet our expectations, it makes it much easier to declare a winner,” Stephen Ohlemacher, an AP election decisionmaker, told his news outlet last week. “When the votes come in and contradict what our expectations are, that’s when we slam on the brakes. We don’t call a winner until there is no path for the trailing candidate to catch the leader.”

In some states there are varying rules on runoffs and recounts in election races that can make the process a bit more complex, particularly in battleground states.

In Georgia, for example, the race between Sen. Raphael Warnock (D) and Republican nominee Herschel Walker could go to a runoff if neither candidate receives more than 50 percent of the vote.

Similarly, Alaska is likely to be the last state to report its unofficial results because of its ranked-choice voting system, in which voters rank candidates in terms of preference. A candidate must receive more than 50 percent of the vote to win.

Ultimately, the most important thing for election callers is accuracy, not speed.

In the 2020 election, the AP says it was 100 percent accurate in calling presidential and congressional races, the same bar the organization will hold itself to on Tuesday.