Presidential election results are announced on a state-by-state basis, with states on the eastern coast typically being announced first and western states being announced later. While news anchors typically announce who has won a specific state over the airwaves, the two main organizations who actually make the official call are Reuters and The Associated Press.
Election Results by State
Current Presidential voting results and electoral college numbers are updated live as soon as Reuters and/or The Associated Press determine a candidate has won the state. These two organizations take a number of factors into account before making an official announcement for a given state, including the states voting history, demographics, and exit polls conducted outside of polling stations and over the telephone.
Many states are considered "safe states" for a Democratic or Republican candidate and will be called within minutes of the polls officially closing, but a number of states aren't as easy to predict and may take some time before a winner can be safely announced.
One of the biggest things that could delay an official announcement in a state is the amount of mail-in ballots and, perhaps more importantly, whether mail-in ballots can start being counted before election day or not. Twenty states have laws that allow the counting of mail-in and absentee ballots before election day, which means thirty states along with Washington, D.C. do not begin to count their ballots until some point during election day itself.
Ballots cast in person before and on election day are counted in real time and are immediately known to election officials and trained local experts.
After all of the above is taken into account and experts are confident in their decision, a state is "called" for a candidate and then announced to the public.
Premiere Real Time Presidential Election Results Organizations:
The Associated Press
Reuters
FiveThirtyEight
CNN
ABC/NBC/CBS
New York Times
Washington Post
Early, Absentee, and Mail Ballots
Thirty-eight states and Washington, D.C. allow some form of early voting and an additional five states vote exclusively by mail.
Individual states are allowed to determine whether or not they will allow early and absentee voting, the number of days it will be allowed, and who is eligible to participate. Some states have very strict rules while others give eligible voters ample opportunity to vote early in person or by mail. Ballots cast early at an official polling site are counted immediately while ballots cast by mail are opened and added to the official total according to state law.
Major media organizations use a variety of tools to accurately report the trajectory of early and absentee votes, especially when state law allows absentee votes to be counted early.
Track Up To Date Early Vote Results By State
Declaring State Winners
A winner is declared in a state when it is clear a candidate has or will have more votes than any other candidate in the state. Typically the winner of a state will be called by The Associated Press and/or Reuters and then relayed to the American people by media outlets.
Forty-eight states and Washington, D.C. have a "winner take all" system for their electoral college votes. That means the candidate who received the most votes in the state will receive all of that states electoral college delegates.
Two states - Maine and Nebraska - award two electoral votes to the state popular vote winner, and then one electoral vote to the popular vote winner in each Congressional district.
The candidate who earns 270 out of the 530 electoral college delegates is declared the winner of the Presidential election.
If a state is too close to call then most, but not all, states allow a candidate to request a partial or full recount of votes cast. In most of the states the person requesting a recount is required to submit a deposit toward the cost of conducting the recount. The deposit is refunded if the recount reverses the result of the election, but if the recount does not change the results then the person requesting the recount will be required to pay most, if not all, of the costs associated with the recount. On the other hand, automatic recounts are paid for by the state or county conducting the recount.
Candidates may also file lawsuits in state and/or federal court if they wish to contest the voting results. State legislators, Governors, and even the U.S. Congress could also get involved in the most extreme scenarios of a contested election.
However, if there is a clear and decisive winner then these worst case scenarios are very unlikely to play out and the candidate who won 270 or more electoral college votes will be inaugurated on January 20 (or January 21 if January 20 falls on a Sunday) after the Presidential election the prior November.