When Democrat Kamala Harris and Republican Donald Trump go head to head in the 2024 US presidential election this week, 270 will be the magic number in both candidates’ crosshairs. That’s the amount of ‘electoral votes’ a presidential nominee needs to secure victory in the race for the White House.

What are electoral votes? What is the Electoral College?

In the US, the general population votes for the country’s president only indirectly. It is actually a body known as the Electoral College that is directly responsible for choosing the new commander-in-chief, through a post-Election Day vote involving a group of ‘electors’ appointed to cast the final ballots.

Numbering 538 - one for every member of the US Congress - these electors are put forward for the job by their party and are given one vote each. “Generally, the parties select members known for their loyalty and service to the party, such as party leaders, state and local elected officials, and party activists,” the National Conference of State Legislatures explains.

Each US state, plus the District of Columbia, is allocated a certain number of ‘electoral votes’ that mirrors its representation in Congress. For example, California has 52 House representatives and two senators, so is given 54 electoral votes. The states and districts with the fewest members in Congress - and therefore the fewest electoral votes - are Alaska, D.C., Delaware, North Dakota, South Dakota, Vermont and Wyoming. This septet has three votes each in the Electoral College.

Almost every state or district hands out its Electoral College votes on a winner-takes-all basis: they are awarded in their entirety to the candidate that prevails in the popular vote in that part of the US.

There are two exceptions to this, however: in Maine and Nebraska, which have five and four electoral votes, respectively, these votes are distributed proportionally. In the 2020 presidential election, for example, Democrat Joe Biden won three electoral votes to Trump’s one in Maine, while Trump took home four votes to Biden’s one in Nebraska.

Because of the US’s Electoral College system, it is possible for a candidate to win the nationwide popular ballot but, depending on the state-by-state distribution of the votes they receive, lose out in the Electoral College. This, for instance, was the case in 2016, when Democratic candidate Hillary Clinton was beaten to the White House by Trump, despite picking up nearly three million more votes on Election Day.

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What happens if no candidate earns 270 Electoral College votes?

With 538 electoral votes up for grabs, each presidential candidate knows that the keys to the Oval Office will be theirs once they reach 270.

But if no nominee secures such a decisive majority of electoral votes - be it because of a tie, or because Election Day success for independent contenders means the candidate with the most electoral votes still falls short of 270 - the House of Representatives decides the winner. This has happened only twice in US history, and not for 200 years. Thomas Jefferson beat Aaron Burr to the presidency by a House vote in 1800, before Andrew Jackson succumbed to John Quincy Adams by the same method in 1824.

In what is known as a ‘contingent election’, each state chooses one presidential candidate from the top three contenders in the popular election. “Representatives of states with two or more Representatives would therefore need to conduct an internal poll within their state delegation to decide which candidate would receive the state’s single vote,” the Congressional Research Service notes. A ‘contingent election’, whose organization falls under the 12th Amendment of the US constitution, should be held on January 6.

When are electoral votes cast?

After the American public has had its say in the presidential election on the first Tuesday of November, the Electoral College meets the following month - on the first Tuesday after the second Wednesday in December, to be precise - to officially cast each state’s electoral votes.

Normally, the ballots cast by electoral voters will reflect the will of the people in their state; however, not every state binds its Electoral College members to do so by law, and it is not unheard of for electors to go rogue. In the 2016 election, for example, there were seven so-called ‘faithless’ electors.

It should be noted, though, that such electoral votes have never had a decisive impact on the result of a US presidential election.