Tens of millions of Americans will cast their vote today, or have already done so, and all either candidate can do now is wait for the result.
But unlike British General Elections, where voters cast one vote for their MP, which then decides which party will have an overall majority and who will be Prime Minister, the US election isn’t quite so simple.
Instead of casting just one vote, each person must vote for their president and state representatives separately.
This can often mean a voter can cast their ballot for a president from one party and their senator from another.
Dr Gina Yannitell Reinhardt from the Department of Government at the University of Essex explains how the US political system differs from here in the UK.
She said: “There are two key differences. In the UK there is a parliamentary system with a Presidential system in the US. In the UK you vote for a party whereas in the US you’re voting for a person.
“You vote for someone to be President, the US senate and your State senate. The outcome may be less straightforward.”
Here in the UK we have adopted a First Past The Post electoral system with the country divided into constituencies, which are each represented by an MP.
The candidate with the most votes then becomes the constituency MP and the political party with the most MPs takes power, with their leader the Prime Minister.
However, in America, the President is decided by the Electoral College system. Instead of voting for a presidential candidate, voters instead cast their ballot for an elector from their State.
Dr Reinhardt explained: “Each State gets a certain amount of votes in the electoral college. There are 538 votes to capture in the electoral college, so they key thing for each candidate is to win States rather than votes.”
This explains how, despite winning almost three million more votes in the popular vote, Hillary Clinton still lost out on the presidency to Donald Trump in 2016.
The candidate who reaches 270 or more of the electors from the electoral college has won the election.
Dr Reinhardt said: “The vote today is a popular vote and it’ll tell us who got the most popular vote but the election hasn’t been determined until the electoral college has voted and that happens a few weeks later.
“When people go to the polls in the US and vote this isn’t an even way to distribute votes. Each State has a certain amount of electors and some have a better ratio than others, for example more electors to the number of voters.
“Some States where the population is small may have something like one elector to every 100,000 voters, while others could have something like one elector to every one million people.
“This means that each person’s vote doesn’t count equally in the vote for the President.”
And there are some key States that candidates need to win to ensure they receive enough votes in the electoral college to be named President.
Florida, Ohio, North Carolina, Iowa and Michigan are all swing States – but the key State that needs to be won is Pennsylvania.
Dr Reinhardt said: “The polls have a margin of error of three percent so in Florida, Iowa, Ohio and North Carolina Biden and Trump are tied.
“But in Pennsylvania Biden is leading by more than the margin of error.”
Some States are very likely to always vote either Democrat or Republican in the electoral college – for example California always goes Democrat along with New York, while Louisiana and Arkansas vote Republican.
So when all the votes are in, rather than each State coming back with a result, the most common outcome is when some of the swing States have declared and it becomes obvious which candidate has won enough votes, their rival concedes the election.
Dr Reinhardt said: “Before the polls have closed on the West coast we might see the election called or at least predicted because we expect some States will vote the same way they always have.
“Rather than waiting for all the States, one candidate can say ‘I’m conceding’ when it becomes clear they can’t win.”
However, this doesn’t always happen.
Dr Reinhardt said: “In 2000 one of the mid-States, Florida, was unclear about who’d won and it ended up going to the Supreme Court.”
Many people are worried this could be the outcome of the 2020 election.
Dr Reinhardt explained: “People are concerned Trump will refuse to condede even if he looks likely to lose. He’ll surely lose the popular vote, he didn’t win it in 2016 and he’s unlikely to win it now.
“There’s also not much chance he’ll win the electoral college, around a one in six chance, so it’s possible he could win, but not likely.
“However, he could refuse to concede and then we will have to wait and see what each State’s results are officially. Also, if we don’t have a concession we can count each State’s precincts carefully.”
Whoever loses the election could also contest the result and challenge it in the Supreme Court, which has just appointed Trump-backed Amy Coney Barrett
Dr Reinhardt said: “This can end up in the Supreme Court and will be up to them to make a decision. The Supreme Court is very conservative and the decision will be taken by three justices.
“I don’t think it’s very likely because I think the election will be decisive enough that the Supreme Court wouldn’t be comfortable invalidating the election.
“I don’t think Trump would have a lot of ground to stand on and there’s a chance he won’t contest the result at all, for example if it’s a landslide and people around him convince him that he would look ridiculous.”