Some 150 million Americans are likely to vote in the US election , but its the votes of just a few hundred thousand people in less than a dozen states that will decide who becomes president.

Thats thanks to the electoral college system. Put simply, this means theres 538 electoral college votes spread over all the US states (and Washington DC), and the first candidate to get 270 votes wins. Each state is assigned a number of votes based on the size of its population and, in all but two states, the candidate with the most ballots takes all. Heres a more detailed guide to how that works.

Many states are highly unlikely to change allegiance. New York and Washington have voted Democratic since 1984, and Alabama and Oklahoma have gone Republican in the last seven presidential elections. So its the swing states that matter.

Donald Trump s unexpected win in 2016 was the result of narrowly winning safe Democrat states in the Mid-West. Some 79,646 votes that made up Trumps combined margin of victory in Pennsylvania, Wisconsin and Michigan in 2016. The polls suggest Joe Biden is winning not just nationally but also in these toss-up states. But its not just these rustbelt states you need to keep an eye on ...

These are the seven big states to watch:

FLORIDA

With its 29 electoral college votes, winning the Sunshine State is essential for the presidential hopefuls. Barack Obama won Florida in 2008 and 2012, and Trump defeated Hillary Clinton there in 2016 by just 1.2% of the vote.

To give it some context, the last Republican to win the White House without winning Florida was Calvin Coolidge in 1924. And in 2016 the election was decided by 113,000 votes from Florida.

A popular destination for retirees, much will depend on whether Trump faces a backlash from seniors over his handling of the pandemic.

If Biden wins Florida, its going to be very difficult for Trump to put together the 270 electoral college votes necessary to win. A Trump win narrows Bidens path, for sure, but he still has more routes to the White House.

Electoral votes: 29

Polls close: 7pm eastern US/ 5.30 am IST (though parts of the state close later)

2016: Donald Trump 49.0% Hillary Clinton 47.8%

NORTH CAROLINA

The southern state has voted reliably Republican for decades, with George W Bush taking the state by double-digit margins in the 2000 and 2004 presidential elections.

But in 2008 Obama snatched the state for the Democrats for the first time since 1976. The Republicans narrowly won it back in the next two elections Mitt Romney in 2012, Trump in 2016. But his year polls suggest Biden could nudge the state and its 15 electoral votes back into the Democratic column, though the result as at recent elections could be very close.

North Carolina and Florida are the two swing states most likely to report prompt results on election night, and as such will give an early indication of how both Biden and Trump are faring.

Electoral votes: 15

Polls close: 7.30pm eastern US/ 6 am IST

2016: Donald Trump 50.5% Hillary Clinton 46.8%