Political calculation: The maths behind the US presidential election

Washington: The US presidential election on Tuesday could hinge on about a dozen so-called swing states where the contest between Democrat Hillary Clinton and Republican Donald Trump is particularly tight.

The victor must get to the magic number of 270 electoral college votes — but just trying to anticipate the result is a complicated exercise in adding, subtracting and combining.

A total of 538 electoral votes are in play, corresponding to the total number of elected representatives in Congress (435 members of the House and 100 senators) plus three for the US capital Washington, DC.

Those who win a state’s popular vote are apportioned the state’s electors, the number of which is roughly in line to the size of its population.

Florida is the mother of all swing states, with 29 electoral votes. It can make or break a candidate, as in 2000, when a few hundred votes separated eventual president George W Bush and Democratic contender Al Gore.

Pennsylvania, with 20 electoral votes, and Ohio, with 18, are also key, along with North Carolina, Colorado and Arizona.

Potentially, candidates could also forge a path to 270 by winning enough small states such as Nevada, Iowa and New Hampshire — or by winning a state that’s historically voted for the opposing camp.

Here’s a list of the major swing states, the number of electoral votes and the averages of recent polls through November 4 in a four-way race — including the outsiders, Libertarian Gary Johnson and Green candidate Jill Stein, and who won the state in the last two elections.