As the polls begin to open across America, it’s time to think about how a candidate actually translates popular support into the keys to the White House. And for people intending to stay up tonight to see the race through to the bitter end, what are they key moments to watch out for?

The presidential race is not decided directly by the popular vote but rather by an Electoral College made up of 538 delegates from all 50 states, plus DC. This group of electors has a constitutional duty to elect the President and Vice President of the United States, and delegates are informed by the votes cast by the public in their respective states so as to do this.

The number of delegates allocated to each state is proportional to its population size and is apportioned in a similar way to the US Congress – the larger the population, the more electoral college votes. With the exception of Maine and Nebraska, the winner of the popular vote in each state gains the votes of all its electors.

A candidate needs to obtain an absolute majority of 270 votes in the College to win the presidency. In the history of presidential elections, there have been four elections where a candidate won the presidency without winning the popular vote. The most recent was the infamous Bush v. Gore election of 2000.

States that swing between voting Democrat or Republican in successive elections are thus vital “battleground” states whose delegates will help a presidential candidate tip the balance in the Electoral College to secure victory.

In the 2016 election, at least 11 such states are polling the candidates closely and will be crucial to winning the presidency. These battlegrounds range from states with a handful of electors, such as New Hampshire with 4 votes and Iowa with 6, to giants such as Ohio (18), Pennsylvania (20) and Florida (29). Estimates suggest Clinton can hope to win approximately 268 delegates from solidly Democrat or Democrat-leaning states, and that Trump is set to win 204 votes from states that have traditionally voted Republican. The outcome of the election will hinge upon these swing states.

Trump’s path to the White House is steep and winding, but success is plausible. In Florida, polls put the candidates at a dead heat with 45.6% of the vote each; its 29 delegates will be enormously significant to the outcome of the race. Pennsylvania and Michigan, states that the Trump campaign has targeted heavily, could both opt for a Republican president for the first time since 1988, collectively adding 36 votes to his total and offering a pathway to victory. Winning in North Carolina, where polls put Clinton ahead by just 0.2%, would crucially add 16 delegates to Trump’s total and put an Electoral College majority within his grasp.

While she does not enjoy the iron-clad lead in the Electoral College forecast earlier this year, Clinton’s chance at an absolute majority is solid. Her large number of estimated delegates makes the path to 270 clearer, and success in a few key swing states would carry her to victory. Securing the “Obama-states” of Ohio, where she trails Trump by 1%, and North Carolina, where last night she held a midnight rally, would deliver her the presidency. The Hispanic voters that make up 17% of Florida’s electorate may clinch that state for Hillary, and early voting in Nevada indicated a surge in Latino turnout that could produce a decisive Democrat swing. Clinton would not need to achieve a political landslide across battleground states like that which would propel Trump to the White House. But as the agonisingly close polls show, her route to victory is by no means certain.

All of this means that we might have an idea of the result by 1am UK time, after exit polls are released from Florida, North Carolina and Ohio. Or we might have to wait for a nail-biting three hours to see how results pan out across the country. Either way, it’s going to be a tense night that mirrors a roller-coaster presidential race.