There have been five United States presidential elections in which the winner lost the popular vote since the 1824 election, which was the first U.S. presidential election where the popular vote was recorded. Losing the popular vote means securing less of the national popular vote than the person who received the largest share of that vote, and does not mean securing less than 50% of the national popular vote.
In the United States presidential election system, instead of the nationwide popular vote determining the outcome of the election, the President of the United States is determined by votes cast by electors of the Electoral College. Alternatively, if no candidate receives an absolute majority of electoral votes, the election is determined by the House of Representatives. These procedures are governed by the Twelfth Amendment to the United States Constitution.
When individuals cast ballots in the general election, they are choosing electors and telling them whom they should vote for in the Electoral College. The "national popular vote" is the sum of all the votes cast in the general election, nationwide. The presidential elections of 1876, 1888, 2000, and 2016 produced an Electoral College winner who did not receive the most votes in the general election. In 1824, there were six states in which electors were legislatively appointed, rather than popularly elected, so the true national popular vote is uncertain. When no candidate received a majority of electoral votes in 1824, the election was decided by the House of Representatives. For these two reasons, the 1824 election should probably be considered distinct from the latter four elections in which all of the states had popular selection of electors, and a single candidate won an outright majority of the electoral votes and thus became president without a contingent election in the House of Representatives. The true national popular vote total was also uncertain in the 1960 election, and the plurality for the winner depends on how votes for Alabama electors are allocated.