US elections explained and key dates on the road to the White House [Infographics]
The big early dates in the road to the White House come during February, as Iowa, New Hampshire and South Carolina voters winnow the fields.
Candidates who don't reach five percent will likely give up.
The first big day is on March 1 , or Super Tuesday, when 14 states, many in the South, as well as Democrats abroad and Democrats in American Samoa vote.
Top that with the prediction that political ad spending will reach a record high of an estimated $11.4 billion during the year.
Democrat candidates Hilary Clinton and Bernie Sanders face up to five months on the road as they battle to win the support of a majority of delegates in each state to secure the presidential nomination.
The Republican camp includes Ted Cruz, Donald Trump and Marco Rubio.
Candidates must win delegates in each state to capture their nomination for the presidency but with over half the contests held in March, the race could be over well before the Republican Convention in July.