For now, at least, Hillary Clinton has a 76 percent chance of defeating Donald Trump to become president of the United States.  A victory by Mr. Trump remains quite possible: Mrs. Clinton’s chance of losing is about the same probability that an N.B.A. player will miss a free throw.  This electoral probability, the first forecast by the Upshot’s presidential prediction model, is based on the voting history of each state and on roughly 300 state and national polls of the race conducted since mid-April.  Our model suggests Mrs. Clinton is a strong favorite in 14 states and the District of Columbia, enough to give her 186 of the 270 electoral votes she needs to win the White House. Add to this eight more states that polls currently show are leaning Democratic — including Minnesota, Michigan and Pennsylvania — and Mrs. Clinton would have 275 electoral votes and the presidency.  But, with 16 weeks remaining in the campaign, a lot can change. Using the same model, we would have said that Bill Clinton had less than a 20 percent chance to win the presidency with roughly four months to go in 1992. It was only after Ross Perot left the race and the Democrats rallied around Mr. Clinton after the Democratic convention that his polls improved. And they improved sharply. One month later, he was an 84 percent favorite.  This kind of polling volatility should be expected, particularly with party conventions at hand. It is one reason that Mrs. Clinton’s probability of victory is not higher. Current polling averages suggest a four-point victory in the national popular vote for Mrs. Clinton, if nothing changes. But we expect changes between now and Election Day.  The Upshot is not the only news organization trying to forecast election results. We believe each model provides useful glimpses of possible futures, so we are compiling forecasts from a variety of them into one easy-to-digest table.  Viewed side by side, the differences among the models become clearer. Arizona, for example, is rated as a tossup by FiveThirtyEight, while our model has not yet seen enough polling evidence to revise its assessment of Arizona’s recent history as a Republican-leaning state. Similarly, while the betting markets rate New Mexico as almost a sure thing in the Democratic column, our model is not as certain, giving Mr. Trump a 21 percent chance to upset Mrs. Clinton there.  We’ll update our forecast every day until Election Day. Check here to see our predictions and that of others, and to play around with the possible paths that could lead Mrs. Clinton or Mr. Trump to victory. Below is more about how we built our model.  The Upshot’s presidential forecast, updated daily.  Our model is slow to move.  This is by design. Our model starts with a weighted average of polls in each state, giving polls conducted more recently and polls with a larger sample size a greater weight in the average. At this point in the election cycle, it uses a longer time window to calculate these averages. This steadiness means it is more stable and less inclined to chase after the most recent poll. But it also means it is slower to react to developing trends, such as recent polling that may indicate a tightening race. This can be a feature or a bug, depending on your perspective. Preconvention polls are informative, but history suggests that it is a mistake to place too much emphasis on a week’s worth of polling.  Let’s say you want to forecast the average margin of national polls for the next month. Would you rather take the average of the polls from the previous two weeks or average every poll from the previous two months? More often than not, you’d be better off taking the average of the longer period. This informs the approach taken by our model.  That said, we expect the simulations in our model to converge rapidly over the next month or two, as the conventions end and polling becomes more predictive of the final outcome.  Distributions are more interesting than averages.  Our estimate for Mrs. Clinton’s lead over Mr. Trump nationally is 3.7 points; our friends at FiveThirtyEight have a slightly smaller estimate of 3.4 points, but our overall probabilities of winning differ by 12 percentage points. This is a small difference, but a notable one. We believe one source of the difference is in the ways we believe states will (or won’t) swing together, and how much they’ll shift.  This is illustrated best by seeing our electoral distributions side by side: The FiveThirtyEight histogram is wider and flatter than ours. It assigns a greater chance that something highly unusual will happen, while ours thinks that the course of this election will look pretty much like the ones that have come before it. For example, we think there is only about a 1 percent chance that Mrs. Clinton will get fewer than 160 electoral votes. The FiveThirtyEight model assigns that prospect an 8 percent chance.
Introducing our forecasting model, which doesn’t put much stock in so-called fundamentals; it’s based almost entirely on polls.