When will we know the result of the US presidential election?

Over the last 25 years, Americans have regularly found themselves up into the early morning hours waiting for news organizations to make the decisive call of the last state needed to put a presidential candidate in the White House, and to learn who controls Congress.

A moment like this on election night in 2000 led to our common language of Republican states as red states and Democratic states as blue states, as the US watched the Meet the Press host Tim Russert on NBC talk late through the night about what was happening in Florida.

It’s extremely unlikely that we’ll know the winner of the presidential contest on election night, as Kamala Harris and Donald Trump are virtually tied in the polls, and the odds that the race comes down to a small number of swing states is high.

So when will we know who won the US election?

Well, that depends on how close things turn out to be. Four swing states – Arizona, Nevada, Pennsylvania and Wisconsin – have absentee ballot procedures that can require days to conclude. But if Harris has decisively won the other swing states, it is enough to declare her the victor. Any other result will take time.

Why do US news organizations make the call?

News organizations call a winner. They do not determine a winner. Officials in elections offices who count votes and certify election results determine the winner. That certification happens days or even weeks after an election.

News organizations convey the moment it has become plain from what those elections offices have said that the mathematical results of the vote count show a winner.

“Our standard is absolute certainty,” said David Scott, head of news strategy and operations at the Associated Press. “We don’t declare a winner until we are 100% confident that the trailing candidates can’t catch up.”

The Guardian follows the Associated Press in calling an election.

How do news organizations make their calls?

The AP and other election night news organizations such as CNN, NBC, ABC and Fox News maintain a “decision desk” and use a model to project how the vote count will unfold, state by state. Some are now relying on Decision Desk HQ, an independent organization set up specifically for this task.

“News organizations have gotten a lot more nervous about making early calls because they don’t want to have to take a call back like they did in 2000,” said Mike Whener, a professor studying elections at the University of Wisconsin.

The decisions about when to call are made by statisticians, not news anchors.

“It’s not Sean Hannity making that determination,” Whener said. “It’s not Rupert Murdoch making that determination early. It’s the people in the room doing the analysis, making that determination about whether, whether the election can be called.”

The calls of different networks may differ in timing because each uses a model that is independent of others. Different analysts may make conclusions at different times.

When did we know the results in 2020?

Joe Biden was declared the winner on Saturday 7 November – four days after the election. The president crossed the electoral vote threshold that day when media outlets called Pennsylvania and Nevada. Michigan and Wisconsin were both called the day after the election, but Arizona wasn’t called until 12 November, North Carolina until 13 November, and Georgia on 19 November, after a recount.

Will results be faster or slower than 2020?

That depends on the margins in each state. According to Protect Democracy, a non-partisan group, we’ll generally see results faster than in 2020 if the margin in a state is greater than 0.5%. They draw this conclusion because there will be significantly fewer mail ballots than in 2020, and states will be able to count them faster. Three states also expanded the pre-canvassing of mail ballots before election day that didn’t in 2020 (Arizona, Georgia and Michigan) and three states have an earlier deadline for when mail ballots must arrive than they did in 2020 (North Carolina, Nevada and Pennsylvania).

Protect Democracy said in a recent report that its best guess was that results will be called in Michigan and Wisconsin one full day after polls closed – the same speed as 2020. It also guesses that Pennsylvania will be called faster than in 2020, when it took four days; Nevada will be called in the same amount of time or faster than 2020, when it took four days and Arizona will also be called in the same amount of time or faster than 2020, when it took nine days. North Carolina and Georgia will both be called faster than 2020, the organization guesses.

What could prolong results?

If the margin in states is smaller than 0.5% or if any states require recounts, results could be prolonged. News outlets will generally not call states until the results of a recount.

For Arizona and Nevada in particular, “it’s very unlikely anybody’s going to call those races on election night,” McCoy said. “That’s the way those states have worked for a very long time, and so that’s very much expected.” If another swing state is as close as Georgia was in 2020, “you’re just waiting. That’s not something you’re going to get ahead of and make a projection that’s just too close to call. And so you’re just waiting for the votes to come.”

Pennsylvania is particularly challenging because by law, local elections offices can’t begin opening envelopes and tallying mail-in ballots until the day of the election. Wisconsin, another swing state, has a similar restriction and may not report complete results until early Wednesday morning.

Some states permit absentee ballots to be counted as much as 10 days after election day. Of the swing states, only Nevada has a meaningful delay; it can accept mail-in ballots up to the Saturday after election day, as long as they are postmarked by 5 November.

If there are legal battles over which ballots to count, that could also delay results. There are currently numerous pending lawsuits in a number of swing states concerning the canvassing of certain ballots, including late-arriving ballots and overseas ballots.

If a state has results like Florida in 2000, where a three-digit number separates two candidates, the result may come down to military absentee ballots and possibly provisional ballots. Typically, only about half of provisional ballots count, but in a close race we’ll see a mad scramble by political teams to find the people who cast those ballots to “cure” them, which usually involves bringing proof of identification and registration to an elections office.

What states will provide results first this year?

It’s likely that news organizations will call several east coast states first where one candidate has a clear advantage over the other.

“Obviously, there are some states that are going to be basically called at full closing,” said Drew McCoy, president of Decision Desk HQ. “There’ll be some that are called, you know, once you sort of start to see the first votes come in and that it tracks with historical precedents.”

What is the ‘red mirage’ and the ‘blue shift’?

The phrases “red mirage” and “blue shift” refer to the same phenomenon in which a Republican candidate appears to have a lead early in the evening, only for that edge to disappear as more votes are counted.

In 2020, mail-in ballots heavily favored Democrats, while Republicans were far more likely to vote in-person. On Wednesday at noon on the day after the election, Donald Trump had an 11% lead, which Joe Biden overcame over the next two days as elections workers counted 2.7 million voters’ mail-in ballots. The AP and other news organizations knew how many absentee ballots voters had returned, and knew how many had been requested by registered Democrats, and refrained from calling the race for Biden until those ballots were counted.

On the Friday before election day, Wisconsin had received more than 1m absentee ballots, with more on the way.

“In the two most populous counties, they don’t finish counting until 1am or 2am,” Whener said. “And so several hundred thousand votes come in, you know, under the cover of darkness, and they happen in the two most liberal counties in the state. The Democrat always picks up a ton of votes in the middle of the night in Wisconsin, because, by law, they can’t start counting until then. It’s a petri dish for conspiracy theories, even though they’re doing things exactly the way they’re required to do them.”

The opposite phenomenon occurs in Arizona, where mail-in ballots received before election day are counted – and reported – first. In 2022, the Democratic senator Mark Kelly had a 20-point lead over Republican Blake Masters at the start of the night. Kelly ultimately won with a five-point margin.

But mail-in ballots received on election day cannot be processed until after the polls close. In 2020, that was a significant number – about 320,000 ballots in Maricopa county alone.

Why is this so complicated? Why doesn’t the country just add up all the votes and see who has more?

A reminder: in the presidential election contest, the popular vote nationally does not determine the result. Each state counts its votes separately. With two exceptions – Nebraska and Maine – the winner of a state gets all of its electoral votes, regardless of whether the state was won by 537 votes out of about 6m cast, as in the presidential contest in Florida in 2000, or the 1.5m-vote margin Reagan won California by in 1984.

Each state has a number of electors based on the number of congressional districts it has, plus two additional votes representing the state’s Senate seats. Washington DC has three electoral votes, despite having no voting representation in Congress.

It takes 270 electors to win.

Biden won by a 51-47 percentage in 2020, a margin of about 7m votes. The electoral count was 306-232, winning about 57% of the electors.

When will we know who controls Congress?

Individual congressional races will be called as votes come in, but with 435 races across the country, some are bound to be too close to call on election night. Depending on how many, it may not be obvious for some time which party controls Congress, McCoy said.

“There’s always kind of like one or two races that are just, you know, ridiculously close, and it just goes to a recount, or whatever the process may be,” McCoy said. “It’s very much about waiting for the data and seeing what it tells you, not getting in front of that. That’s our biggest rule, is never getting in front of the data.”