A handful of states will play a crucial role in determining the outcome of the 2024 US presidential election.

These are the “swing states”: so called because they will help swing the overall outcome either toward Democratic candidate and current Vice President Kamala Harris, or away from Ms. Harris and toward her Republican opponent – ​​and former president – ​​​​Donald Trump.

Most states are not swing states and will not change hands in this election – but safe states alone are not enough to bring Ms. Harris or Mr. Trump to the White House.

Here are seven swing states to watch.

All but one were won by President Joe Biden for Democrats in 2020, but all are strongly contested in this election by Mr. Trump.

Donald Trump won Pennsylvania in 2016, confounding those who thought it was a Democratic stronghold, as it had in every election since Bill Clinton won the state in 1992.

Joe Biden narrowly won it back for Democrats in 2020, but polls suggest the outcome this year is on a knife’s edge.

A total of 270 electoral votes are needed to win the United States presidential election, with each state being allocated a fixed number of votes based approximately on its population size.

Whoever wins the popular vote in a state also wins all of that state’s electoral votes (with two exceptions, Maine and Nebraska, where votes are distributed at the district and state level).

With 19 electoral votes up for grabs in Pennsylvania, this is a key goal for both candidates.

But due to the large number of absentee and early votes, which will need to be sorted and counted, the outcome will likely not be clear for some time.

In 2020, the state was not called for Mr. Biden until four days after Election Day.

Like Pennsylvania, it was part of the “blue wall” of states that voted Democratic in every presidential election from 1992 to 2012.

Mr. Trump’s victory in 2016 was tiny — just 0.2 percentage points — but symbolized the scale of his success in alienating working-class voters from his opponent Hillary Clinton, particularly in a state that Barack Obama won by nine percentage points in 2012.

Joe Biden won the state back for Democrats in 2020 with a nearly three-point margin over Mr Trump, but opinion polls suggest it will be much closer this time.

There are 15 electoral votes at stake here.

This is another “blue wall” state that narrowly turned to the Republicans and Donald Trump in 2016, before swinging back – by an equally narrow margin – to the Democrats and Joe Biden in 2020.

As is the case in Pennsylvania and Michigan, the outcome in Wisconsin may not be clear for several days, due to the volume of mail-in and early votes that will need to be sorted and counted.

Ten electoral votes are available here.

In 2020, Joe Biden was the first Democrat to win Arizona since Bill Clinton in 1996.

This represents a major turnaround from 2016, when Donald Trump beat Hillary Clinton in the state by more than three percentage points.

Mr Biden’s victory was razor-thin and this year the state once again appears to be biting its nails, with polls suggesting the result is too close to call.

Arizona is worth 11 electoral votes.

Nevada has been won by Democrats in every presidential election since 1992, but often by tight margins – and this year it could be tighter than ever, with polls suggesting the race is effectively tied.

Joe Biden won the state in 2020 by just over two percentage points.

Nevada doesn’t offer a large number of electoral votes — six — but in a close contest, a victory here could be decisive in helping Ms. Harris or Mr. Trump reach the White House.

It is the only swing state on the list that was won by Donald Trump in 2020, although the result was close, with Mr. Trump receiving 49.9% of the vote and Joe Biden 48.6%.

North Carolina hasn’t been won by a Democrat since Barack Obama took the state in 2008 – the first Democrat to do so since Jimmy Carter in 1976.

Once again, this year’s opinion polls predict a close fight, with 16 valuable electoral votes up for grabs.

North Carolina is the swing state most likely to report quick results on election night and, as such, will give an early indication of where Ms. Harris and Mr. Trump fare.

In 2020, Joe Biden was the first Democrat to win Georgia since Bill Clinton in 1992.

Barack Obama never came close to victory, and Donald Trump won by more than five percentage points in 2016.

The result in 2020 was so close that a recount was conducted, with the result not confirmed until more than two weeks after Election Day.

Just 0.3 percentage points separated Mr. Biden from Mr. Trump.

As in North Carolina, the state gives its winner 16 electoral votes, and opinion polls here, as elsewhere, point to another incredibly close contest.

But polls are only snapshots, not predictions, and ultimately the outcome in places like Georgia could depend on which side can convince the most of its supporters to turn out to vote.