Voters in the US go to the polls on 5 November to elect their next president.

The election was initially a rematch of 2020 but it was upended in July when President Joe Biden ended his campaign and endorsed Vice-President Kamala Harris.

The big question now is – will America get its first woman president or a second Donald Trump term?

As election day approaches, we’ll be keeping track of the polls and seeing what effect the campaign has on the race for the White House.

Harris is ahead of Trump in the national polling averages as shown in the chart below, with the latest figures rounded to the nearest whole number.

In the months leading up to Biden’s decision to drop out, polls consistently showed him trailing former president Trump. But the race tightened when Harris hit the campaign trail and she developed a small lead that she has maintained since.

The two candidates went head to head in a televised debate in Pennsylvania on 10 September that just over 67 million people tuned in to watch. A couple of snap polls released immediately after the debate found that most viewers thought Harris had been the better performer.

A majority of national polls carried out since then suggest that Harris has made some small gains and while her polling average hasn’t moved much, her lead increased slightly from 2.5 percentage points on the day of the debate to 2.9 points a week later.

That marginal boost was mostly down to Trump’s numbers though. His average had been rising ahead of the debate, but it fell by half a percentage point in the week afterwards.

You can see those small changes in the poll tracker chart below, with the trend lines showing how the averages have changed and the dots showing the individual poll results for each candidate.

While these national polls are a useful guide as to how popular a candidate is across the country as a whole, they’re not necessarily an accurate way to predict the result of the election.

That’s because the US uses an electoral college system, in which each state is given a number of votes roughly in line with the size of its population. A total of 538 electoral college votes are up for grabs, so a candidate needs to hit 270 to win.

There are 50 states in the US but because most of them nearly always vote for the same party, in reality there are just a handful where both candidates stand a chance of winning. These are the places where the election will be won and lost and are known as battleground states.

Right now, the polls are very tight in the seven battleground states, which makes it hard to know who is really leading the race. There are fewer state polls than national polls so we have less data to work with and every poll has a margin of error that means the numbers could be higher or lower.

As is stands, recent polls suggest there are just one or two percentage points separating the candidates in several states. That includes Pennsylvania, which is key as it has the highest number of electoral votes on offer and therefore makes it easier for the winner to reach the 270 votes needed.

Pennsylvania, Michigan and Wisconsin had all been Democratic strongholds before Trump turned them red on his path to winning the presidency in 2016. Biden retook them in 2020 and if Harris can do the same this year then she will be on course to win the election.

In a sign of how the race has changed since Harris became the Democratic nominee, on the day Joe Biden quit the race he was trailing Trump by nearly five percentage points on average in these seven battleground states.

The figures we have used in the graphics above are averages created by polling analysis website 538, which is part of American news network ABC News. To create them, 538 collect the data from individual polls carried out both nationally and in battleground states by lots of polling companies.

As part of their quality control, 538 only include polls from companies that meet certain criteria, like being transparent about how many people they polled, when the poll was carried out and how the poll was conducted (telephone calls, text message, online, etc).

You can read more about the 538 methodology here.

At the moment, the polls suggest that Kamala Harris and Donald Trump are within a couple of percentage points of each other in battleground states – and when the race is that close, it’s very hard to predict winners.

Polls underestimated support for Trump in both 2016 and 2020. Polling companies will be trying to fix that problem in a number of ways, including how to make their results reflect the make-up of the voting population.

Those adjustments are difficult to get right and pollsters still have to make educated guesses about other factors like who will actually turn up to vote on 5 November.

Written and produced by Mike Hills and Libby Rogers. Design by Joy Roxas.