Election Day is Tuesday, but Americans may have to wait longer to find out who their next president will be.

The timing of a Kamala Harris or Donald Trump victory depends on two factors: how quickly states count their ballots and how close the results are. Each state has its own rules for processing and counting ballots.

As polls close across the country – first on the East Coast – and the results are in, news outlets and broadcasters will be projecting the winner of each state and the District of Columbia at the presidential level, as well as races for the U.S. Senate and House of Representatives. The Financial Times will report the results based on calls from the Associated Press.

The most important number on election night is 270, the Electoral College votes needed to win the presidency. A long night awaits you on Tuesday.

Will we find out the winner this evening?

That's unlikely.

Polls suggest results will be close in battleground states, meaning it could be days before a winner is announced. Some states also count ballots more slowly than others.

An additional complication could be legal challenges to a state's results, which could delay the announcement of a winner. The Trump campaign and its allies have already begun to cast doubt on the integrity of the election.

The Harris campaign predicted Trump would declare victory before the presidential race was called.

The first polls close at 6 p.m. Eastern Time on Election Day in some counties in Indiana and Kentucky, while the last polls close at midnight ET in Alaska.

If the swing states start counting quickly and the vote isn't as close as the polls predict, the result could be clear by Tuesday evening. But election experts and state officials predicted it was more likely to come Wednesday morning. In some cases, final results can take days or even weeks as absentee and absentee ballots are counted and occasionally recounted.

It is also likely that it will remain to be seen which party will control the two chambers of Congress, the Senate and the House of Representatives.

According to the nonpartisan Cook Political Report, there are four extremely competitive Senate races and 22 House races where there is no agreement. The Senate map “highly points to a (Republican) majority” while the House battle “remains as close as ever,” CPR's Erin Covey wrote.

Which states are the key to victory?

The key states to watch are the seven battlegrounds: Arizona, Georgia, Michigan, Nevada, North Carolina, Pennsylvania and Wisconsin, which together have 93 electoral votes.

Not every swing state needs to be called to appoint a president. For example, if Harris or Trump were to win the so-called blue wall states – Michigan, Pennsylvania and Wisconsin – and North Carolina overnight, that would be a relatively quick path to 270.

North Carolina could be the first battleground to be declared because most people vote in person and mail-in ballots must arrive by Election Day. A special topic this year is the effects of Hurricane Helene, which hit the state hard.

Georgia is also counting quickly, but its razor-thin lead of 11,779 in 2020 led to a hand count and the state wasn't called for Biden until more than two weeks after the election.

The strength of the blue wall could indicate that a candidate is doing well with working-class voters, while a win in Georgia could be a good sign that he has won over black voters.

Pennsylvania is slow because it can't start counting mail-in ballots until Election Day. Wisconsin also can't begin counting mail-in ballots until Election Day, but officials expect a result Wednesday morning because counting must continue throughout the night. Michigan could move more quickly than before because more mail-in ballots can be processed before Election Day.

Arizona and Nevada are expected to be the slowest in terms of results. Arizona officials said it could take 10 to 13 days for complete results. In Nevada, many people vote by mail.

What happened in 2020?

It wasn't until Saturday, November 7, 2020, four days after Election Day, that Joe Biden was declared the winner. AP made the call at 11:26 a.m. ET.

The AP began calling races starting at 7 p.m. on Election Day, starting with Kentucky. Races in battleground states took much longer — the AP called North Carolina 10 days after Election Day and Georgia 16 days later.

Pennsylvania was the state that pushed Biden over the top, while Georgia and North Carolina were too close to make a decision at that point. In total, Biden won six of the states considered battlegrounds this year, with Trump only winning North Carolina.

On January 6, 2021, while Congress was certifying the results of the election, a mob of violent Trump supporters attacked the US Capitol in an attempt to stop the proceedings and overturn Biden's victory. Democrats cite the events as evidence that Trump threatens democracy if he is re-elected.

In 2016, the AP declared Trump the winner over Democrat Hillary Clinton at 2:29 a.m. ET on Wednesday, November 9, the day after the election. Wisconsin was the state that pushed Trump over the top, while Arizona and Michigan were still too close to call.

What's different this time?

The biggest difference is that there is no pandemic.

2020 saw a surge in early voting as people tried to avoid contracting Covid-19 at the polls on Election Day.

That complicated the counting effort for state election officials because many were unaccustomed to handling large volumes of mail-in ballots, which take longer to tally because they have to be opened and checked by poll workers. Some states also had social distancing rules for election officials, which also slowed counting.

Fewer people have voted early — both in person and by mail — so far than in 2020, meaning state election officials could have a more manageable flow of early ballots to process, speeding up results.