When will we know who will be called as America's next president?

The short answer: By 23:00 EST which is 04:00 GMT.

State projections are likely to be announced between 19:00 EST and 20:00 EST (01:00 GMT).

But, it depends how it goes. If huge numbers sway one way or another, the result will become clear earlier. Some say the result could be called while some ballots are still being cast.

Is the result official?

No. Counting every single vote could take several days.

So how is it decided?

American media calls it.

Each network is under pressure to get it right with research teams. They use what are known as "decision desks", which employ statisticians and pollsters to project the outcome.

LIVE: Election results minute by minute

The Associated Press news agency, NBC, CNN, Fox News and Edison Research carry out exit polls, which help the networks to predict the results.

Has a presidential election result ever be called incorrectly?

Yes. In 2000, when they blew a call on the Florida election results - twice. On the second occasion, they prematurely declared that George W Bush was the next president. 

Source: Al Jazeera News