US Election Night: How to tell if Kamala Harris or Donald Trump is winning

• US Election night betting guide as markets react to early trends

• Swing states and counties to watch and how to interpret results

• Get the latest data including current prices and volume of bets in our daily update

• View Betfair Exchange politics markets as you have never seen them before

US election day is here and more than 77 million votes have already been cast. Today, hundreds of millions of Americans will head to their local polling station to play their part in this unprecedented race for the White House between Donald Trump and Kamala Harris.

We all know how crucial the seven swing states are, and for the past month that's all pollsters, commentators and the candidates have been talking about.

Expect betting market volatility on US election night

Betting in-play on the US election can be very fruitful. As the votes come in overnight the markets are incredibly volatile, and not just the overall winner market.

In fact, overnight four years ago, Joe Biden went out to as big as 100/1101.00 to win in Georgia, the state that ultimately turned the tide for him and swung the race back in his favour.

The market undervalued just how many mail-in votes Biden would get, and while those kinds of votes are down compared to four years ago, there's still a chance of the market doing something similar when it comes to the late counted ballots.

What do we know about the US election early vote?

More than 77 million votes have already been cast, which is below 2020's 101 million, but it is still substantially higher than in 2016 and 2012.

Traditionally, early voting has favoured the Democrats, but compared to 2020, the Republican registered early voters are up. Those with an affiliation to Kamala Harris' party make up 41% of those 77 million, while there are 39% GOP registered early voters, and 20% other.

More women have registered to vote early, compared to men, which you would assume is promising news for Kamala Harris. A massive 53% of early votes have been cast by women, compared to 44% by men.

What to look out for on US election night

If you're going to be glued to the TV and are looking to get involved in the action in-play overnight, here are some of the most important results to look out for when it comes to working out how the swing states, and ultimately the election could go..

Wisconsin's bellwether county - Door County

During my tour across the Blue Wall, a local in Milwaukee told me I should look up Door County if I really wanted to know who was going to win the election. He wasn't wrong. The voters in the 'Cape Cod of the Midwest' have correctly backed every winning president this century.

Wisconsin has voted for last four Presidents, so there's a good chance that whoever wins in Door County will also win Wisconsin and take the White House.

With a population of just over 30,000 the results in Door County should come in relatively quickly.

Michigan's county on the money - Saginaw County

Another successful bellwether county, Saginaw has been the focus for both candidates in their final days of campaigning. Harris was there on Monday, and Donald Trump's running mate JD. Vance was there yesterday.

The county has picked the winner of the last four presidential elections, but the past two have been incredibly tight. Trump won by just over 1,000 votes in 2016, before Biden flipped it back by just 303 votes.

Georgia's battleground indicator for Harris - Baldwin County

This was an incredibly tight race four years ago, one which Biden held for the Democrats, winning by 237 votes.

There's a lot we can read into a result here. The demographic make-up of Baldwin County is almost split between white and black voters, therefore if Harris holds on to this county it is very positive news for her campaign and it will likely signal that she's doing well with black and younger voters.

The county has voted Democrat in each of the last four presidential elections, so if Trump wins here it will be bad news for Harris and likely signal that Georgia is flipping back to the Republicans.

North Carolina Republican stronghold on the slide - Cabarrus County

The last time a Democrat won in Cabarrus County was 76 years ago, when Harry Truman triumphed. While Trump had the backing of voters there in the past two Presidential elections, his support has been on the slide.

Trump won by more than 20% in 2016, but that lead was reduced to single digits four years ago when Biden lost by 9%. If this slide continues and drops to under 5% then Harris is on for a good result in North Carolina.

The county has also reported 10,000 more registered voters than there were four years ago, so this could also give us an insight into how new voters are leaning, which can give us a hint in other key swing states where new registrations are up.

Another North Carolina indicator - Nash County

The only county to elect the winning president three times in a row is Nash County. It voted Obama in 2012, Trump in 2016 and Biden in 2020. So they're a good bellwether to add into the mix here to keep an eye on.

If both Cabarrus and Nash match up with electing the same candidate, that should give us a solid outlook on who things are going for in North Carolina.

Pennsylvania's swing county - Erie County

The state we're all looking at is Pennsylvania. It's huge for Trump if he wins there. Realistically, he needs to split the Blue Wall to win and those 19 electoral college votes will be massive for both candidates.

Erie county, nestled in the north west corner of the state has backed the winning president in the last four elections. It's predominantly made up of white, blue-collar voters - a group that have been withdrawing support from the Democrats in favour of Trump over the past eight years - and can give us insight into how Harris is performing with that demographic.

If she wins there, it bodes well for her across the rest of Pennsylvania and other blue-collar areas of the Rust Belt.

Mail in votes will come late and could swing results

Ultimately, ballot processing times will determine when we get a clear picture of who has won the US election. The ballots that take the longest to process are mail votes.

Four years ago, this was a slow process in Pennsylvania and Wisconsin, as they were unable to start processing them until election day, and we are going to have a similar situation in those states again.

The good news is that Michigan has passed a law to allow the mail vote count process to start much sooner, so we should know how things are going in the Great Lakes State earlier in the night.

I've said this could come down to Pennsylvania. The biggest thing to watch out for is a good start for the Republicans, before those mail in votes are counted. Traditionally, Democrats are more likely to vote early and via mail ballots, so we could see the market heavily shift in Trump's favour before a potential blue wave of early votes which swing things. That is what happened four years ago.

Republican early registration is up on four years ago, but will it be enough to subside any potential blue wave of late counted ballots? We'll find out in the next 24 hours.

Now read Betfair's US Election Live Blog for the latest updates