US election polls: Who is ahead - Harris or Trump?

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.

Who is leading national polls?

Harris has been ahead of Trump in the national polling averages since she entered the race at the end of July, as shown in the chart below with the latest figures rounded to the nearest whole number.

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 majority of national polls carried out in the week after suggested Harris's performance had helped her make some small gains, with her lead increasing from 2.5 percentage points on the day of the debate to 3.3 points just over 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.

Who is winning in battleground states?

Right now, the polls are very tight in the seven states considered battlegrounds in this election with just one or two percentage points separating the candidates.

That includes Pennsylvania, which is key as it has the highest number of electoral votes of the seven states and therefore winning it makes it easier to reach the 270 votes needed.

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

One thing to note is that there are fewer state polls than national polls being carried out at the moment so we have less data to go on and every poll has a margin of error that means the numbers could be higher or lower.

But looking at the trends since Harris joined the race does help highlight the states in which she seems to be in a stronger position, according to the polling averages.

In the chart below you can see that Harris has been leading in Michigan, Pennsylvania and Wisconsin since the start of August.

All three 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.

How are these averages created?

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 collects the data from individual polls carried out both nationally and in battleground states by lots of polling companies.

As part of its quality control, 538 only includes 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.

Can we trust the polls?

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.

-BBC