THIS year's large numbers of postal votes - 50.3 per cent - mean the traditional point when it becomes clear who has won the race for the White House may not be reached on election night.
If there is no clear winner from polling station counting then counting mail-in votes could take days or even weeks, with states like Ohio counting late ballots as long as they are postmarked by November 3.
In previous elections the winner has usually been clear by 4am GMT when the West Coast polls close.
Polls close in North Carolina at 12.30am GMT and will likely see speedy projections due to a large number of early in-person voters. It was won narrowly by Donald Trump in 2016 and is again on a knife-edge. A win potentially signals a good outcome for that candidate.
Polls close in Florida at 1am GMT - a battleground state which has been both a presidential winner and loser. It will report early in-person and postal ballots first - predicted to favour Democratic challenger Joe Biden.
At 2am GMT polls close in Arizona, a state won by Mr Trump in 2016, but with a slim lead for Mr Biden in polls. Early counts are expected to favour Democrats who are more inclined to vote early or by mail.
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Some key states do not count a single ballot until election day so despite Ohio closing polls at 12:30am GMT there will only by preliminary results available until as late as November 28. The state has backed the winner at all but one presidential contest since World War II.
Polls in Pennsylvania, another battleground state, close at 1am GMT and it was here in 2016 that Donald Trump's victory was emphatically comfirmed in 2016 at 6.35am GMT by a single percentage point.
Wisconsin and Michigan will see polls close at 2am GMT, both seen as critical to victory.
If one candidate secures an overwhelming victory, the announcement will come in the early hours of tomorrow morning, but early tallies could be misleading due to the different ways states count in person and postal votes and Deomcratic and Republican voting preferences.
