After polls close in the US presidential election, it could take days or even weeks to find out if Donald Trump or Joe Biden has won.
In this election, millions more Americans have been voting by post because of coronavirus, meaning a delay in counting all the votes is highly likely.
When do we usually get a US election result?
The result is usually called on the night of election day, which this year is Tuesday 3 November.
Different states stop voting at different times. The first polls close on the East Coast at 19: 00 local time (00: 00 GMT).
This is followed by a running total of votes as they are reported in each state.
The full count is never completed on election night – but enough votes are usually in to confirm a winner.
A state is “called” by major US media outlets when they believe one candidate has an unbeatable lead.
But at this stage, when most but not all of the votes will have been counted, this is a projection, not the final result.
US presidents are not decided by the national vote, but by winning enough states.
The winner in each state takes a certain number of “electoral votes” based roughly on the size of its population.
To win the White House, 270 electoral votes are needed.
In 2016, the election was called for Donald Trump at about 02: 30 EST (07: 30 GMT), after victory in Wisconsin put him over the 270.
Why is this year different?
The coronavirus pandemic means more people than ever are voting early, either by post or in person.
Postal votes typically take longer to count as they have to go through more steps to be verified, such as a signature and address check.
Some states, such as Florida and Ohio, allow this process to start weeks before election day, so the votes are ready to be counted.
In these states, it may be possible to call a winner on election night, depending on how close the races are.
But other states, such as Pennsylvania and Wisconsin, don’t allow early votes to be processed until polling day.
These states could be crucial – and election officials have said counts could take days.
The way certain states process votes is also likely to skew early counts:
- In states that wait until election day to process postal votes, initial numbers are likely to favour President Trump as more Republicans are expected to vote in person on polling day and these votes will be quicker to count
- In states that process early votes before election day, the initial numbers are expected to favour Mr Biden as more registered Democrats than Republicans have voted early
This is why election officials have warned the early results may not provide the full picture.
There have been delays in other polls this year – the 23 states that had held election contests after mid-March had taken an average of four days to report nearly complete results, a Washington Post analysis found.
What else might delay the count?
About half of states will accept postal ballots that arrive after election day, as long as they are postmarked by 3 November, so some votes won’t be counted until days after the election.
There’s also expected to be a rise in provisional ballots – votes cast by people who requested a postal ballot but decided to vote in person instead.
And these won’t be included in the initial count, as they require checks to ensure people don’t vote twice.
Will things be normal at polling stations?
Millions of people will still be turning up to vote on election day – but fewer polling stations than usual will be open partly because of coronavirus considerations, and concerns have been raised about worker shortages, meaning long queues are likely.
Familiar problems such as faulty voting machines could also cause delays.
How are votes counted?
Most ballots – paper or digital – are counted by machines.
But poll workers need to check any paper ballots the machines fail to process.
After polls close, the voting data will be transferred to a central election headquarters – a city hall or similar location.
Sometimes, this is done electronically.
But elsewhere, memory devices holding the voting data must be physically delivered or the results read out over the phone.
Once the vote tallies are delivered, they’ll often start to show up on a state’s official website.
When enough votes have been tallied from across a state to determine an unbeatable lead, news organisations call a winning presidential candidate for that state.
These unofficial results are certified only weeks later, when confirmed by state officials.
The final vote tallies can shift between the first count and these certified results but not drastically.
What happens if the election results are disputed?
The pandemic has already led to more than 300 election law cases in 44 states, according the Stanford-MIT healthy-elections project.
And the presidential vote could see legal challenges over everything from identification requirements for postal voting to Covid-related changes to polling systems.
President Trump says the election result could end up in the US Supreme Court.
In 2000, Democrat Al Gore lost Florida and the presidential election by 537 out of a total of almost six million votes.
And this was followed by a highly controversial recount process that lasted over a month – and the Supreme Court ruling in favour of Republican George W Bush.