MAGIC NUMBER: 270
A presidential candidate needs 270 out of 538 Electoral College votes in order to be elected.
In 2012, Barack Obama won 332 electoral votes, well surpassing the 270 to win. The US map below is coloured red (Republican) or blue (Democrat) according to the results of the 2012 US presidential election between Mitt Romney and Obama.
2012 resultsGeographically, it looks like there is more red than blue. But if you scroll down...
You can see the states according to electoral votes, and it is easier to see more blue than red.
What is the Electoral College?
The Electoral College consists of 538 electors, appointed by each state, who will cast their votes for the president and vice-president of the United States.
When Americans cast their votes on Nov 8, they are actually voting for the candidate's electors, who make up this Electoral College.
Learn more Understanding America’s Electoral College
How many electoral votes does each state have?
Each state is awarded at least three electoral votes. Then, depending on its population size, the state receives more electoral votes.
The distribution of electoral votes changes only during each census. There is no change between this year’s electoral votes and those in the last US presidential election.
In most states, the candidate with majority of the popular vote takes all the electoral votes, except for Maine and Nebraska, which don’t follow the winner-takes-all rule.
Democrats historically have relied on big states like California (55 electoral votes) and New York (29 electoral votes), while Republicans have Texas (38 electoral votes) to bolster their numbers.
State of play
Like in any election, there are traditionally safe and swing states.
Safe states - Democrats
Since 1992:
These states have voted Democrat since Bill Clinton was elected president in 1992. Going by this, Hillary Clinton can theoretically hold onto 242 safe Democratic electoral votes. She would still need another 28 electoral votes to secure the presidency.
Safe states - Republicans
Since 1992:
The Republicans, on the other hand, have been able to hold onto these states totalling 102 electoral votes since 1992. Going by this, even with the large state of Texas, Donald Trump would still be 168 votes away from the White House.
Safe states - Republicans
Since 2000:
If Trump were to retain all these states which have voted Republican in the last four elections, this would add an additional 78 electoral votes, bringing his possible total to 180 electoral votes. That’s still 90 votes short of winning the presidency.
Swing states
Since 2000:
These states, coloured purple, have voted Republican and Democrat twice in the past four elections since 2000.
According to The New York Times, if Clinton is able to secure Florida (29 votes) and hold on to the seats the Democrats have won since 1992 (242 votes) she would win the presidency with 271 electoral votes.
Key states to watch
US correspondent Melissa Sim looks at the states to watch.
Pennsylvania
A traditionally Democratic state, but Trump hopes to resonate with the older white, non-college degree voters here.
Acknowledging the importance of keeping this state with 20 electoral college votes in the blue column, the Democrats held their National Convention here in July.
The Democrats will almost certainly take the state, which voted Democrat in the last three presidential elections, according to various forecasts.
But Trump is hoping to make inroads here since the state has a comparatively higher proportion of older white voters without college degrees - a description that fits his voter base.
Still battling for this must-win state, the Trump campaign spent the second highest amount of money (US$938,335) on advertisements in this state from Oct 9 to Oct 15. The highest amount was spent in Florida.
Ohio
Historically, no Republican candidate has won the presidency without carrying this state.
The phrase “As Ohio goes, so goes the nation” refers to the fact that no Republican candidate has ever won the White House without winning the state of Ohio.
As for Democrats, the last person to win an election without taking Ohio was John F. Kennedy in 1960.
The state, which represents 18 electoral college votes, tends to favour political moderates, so candidates cannot be too progressive or conservative if they want to achieve success in the state.
The Republican National Convention was held in Cleveland in July, an acknowledgement of the state’s key role in the race.
While forecasters believed the state would swing to the Republicans last month (Sept), now it looks like the Democrats have a 50 to 67 per cent chance of winning the state, which voted Democrat in the 2012 and 2008 presidential elections, and Republican in 2004.
Read more: See saw battle in Ohio.
Florida
With 29 electoral votes available, this is an important battleground state which could swing either way despite the high proportion of Hispanic and Latino voters.
It has a high proportion of Hispanic and Latino voters but they do not vote as a bloc.
The state is always a battleground because winning it means sweeping 29 electoral votes – the same as New York – which is the third-highest number after California and Texas.
Last month, the state was considered too close to call, but forecasters now have a clearer picture and believe the Democrats have a 73 to 89 per cent chance of winning here. Floridians voted Democrat in the 2008 and 2012 presidential elections, and Republican in 2004.
Nevada
Trump may have an edge with non-college educated voters in the recession-ravaged state despite it being traditionally Democrat because of its racial diversity.
On paper, it should go to the Democrats because of its racial diversity. The Democrats also have more registered party members than Republicans.
But it also has one of the lowest rates of college education, which gives Trump an edge.
Last month, forecasters said that the Republicans were likely to win here, but now the Democrats have a 73 to 84 per cent chance of winning, according to various forecasts.
The state, which has six electoral college votes, voted Democrat in the 2008 and 2012 presidential elections, and Republican in 2004.
North Carolina
Democrats have a slight edge here because of young, educated and relatively wealthy city-based voters.
It voted Republican in the 2012 and 2004 elections, but swung to the Democrats in 2008. According to various forecasts, what used to be a toss-up state has now fallen in the blue column. The Democrats have a 70 to 79 per cent chance of winning here.
Republican candidate Mitt Romney won this state and its 15 electoral college votes in 2012, and Trump must hold on to the state.
But the demographics may not be in his favour. The states’ urban centres are growing, and many of the inhabitants are educated, young and relatively wealthy – a demographic that favours Clinton.
Iowa
A toss-up state where the white farming community is still unsure who to vote for; Trump lost here in the primaries, Clinton won by a small margin.
It voted Democrat in the 2012 and 2008 presidential elections, and Republican in 2004. Forecasters predicted last month that there was a 67 to 96 per cent chance the state would go back to the Republicans, but it has now become a true toss-up state, where the race is too close to call
Trump actually lost the state to Texas Senator Ted Cruz during the caucus, while Clinton won the state only by a razor-thin margin against Vermont Senator Bernie Sanders.
It seems the white farming community is still unsure of who will have their best interests at heart, though Mr Trump may finally be the one to nab the six electoral college votes.
Georgia
A traditionally Republican state that Trump can’t afford to lose. Some polls are edging Clinton slightly ahead.
The state has voted Republican in the last three elections, but it is one of the most vulnerable red states at the moment.
Various forecasts suggest that the Republicans still have a 64 to 89 per cent chance of winning here, but the balance could swing to the Democrats in the coming weeks.
Democratic candidate Hillary Clinton must continue to get out the vote among minorities if she is to win. While not the most competitive state, it is still one to watch.
Arizona
A traditionally Republican state that the Democrats are trying to turn blue. Polls show a statistical tie between the two candidates.
This traditionally red state, which voted Republican in all three of the past elections would be a prize for the Clinton campaign if they manage to pull out a win here.
Forecasters who initially believed the state would remain with the Republicans are beginning to change their tune and say the state is too close to call.
The Clinton campaign recently sent first lady Michelle Obama to campaign in the state, and experts believe Mr Trump may not have sufficient resources to defend a Clinton ambush in the state.