A projection and a sportsbook line are not the same number.
They look like the same kind of number, but they answer different questions. This is a plain, neutral walk-through of what a projection is, what a book's line is, why the two differ, and what people mean when they talk about edge. It holds for an NFL spread, an NBA total, and an MLB moneyline alike, and it carries no numbers and no claim that either one is the last word.
A projection and a line are not the same thing
One is an estimate of how likely an outcome is. The other is a price a business posts to balance the money it takes. Understanding that difference is the whole point of comparing them.
The model projection
An independent estimate
A projection is a forward-looking guess at how an outcome is likely to go, and it blends performance, matchup, venue, weather, and market context into a single number. Its job is to estimate the true likelihood of the outcome.
The sportsbook line
A posted market price
A line is the number a book charges for an outcome. It carries the book's own probability estimate plus a built-in margin, and it moves as bets and news come in. Its job is to balance the money as much as to predict the game.
Vig, market movement, and information
The first reason the two numbers rarely match is the vig, the margin a book bakes into its prices. It is why the two sides of a market do not add up to an even hundred percent. To line a price up against a projection fairly, you strip that margin out to get a "fair" price, which is the market's probability estimate without the house edge.
The second reason is market movement. A line is not fixed, because it drifts as money comes in on one side and as the book manages its exposure. A projection has no such pressure, since it is trying to estimate the outcome rather than balance a book. Even when both start close, they can pull apart through the day.
The third reason is information. Confirmed lineups, an inactives list, a late scratch, changing weather, and injuries all hit a projection and a market at different speeds and in different ways. Two honest attempts to price the same game, working from slightly different inputs and pressures, naturally land in slightly different places.
What people mean by "edge"
Once you have a projection on one side and a de-vigged fair price on the other, the space between them has a name, and that name is edge. When a projection rates an outcome differently than the fair line implies, that disagreement is the edge. It measures relative value and signals that one estimate sees something the other does not.
It helps to be precise about what edge is not. It is not a claim that the projection is right and the market is wrong, and it is not a promise about a single game. A market price aggregates a great deal of money and information, and an independent projection is one more estimate alongside it. Edge simply describes where the two disagree, and by how much.
Neither number is a guarantee
Both a projection and a line are estimates of probability, and probability is not certainty. A projection can be wrong, and a heavily bet favorite can lose. An edge describes long-run relative value, not the result of any one night, which is why it is framed as value and estimate rather than as advice or a sure thing.
The most useful way to hold both is as two opinions, not one verdict, with the projection as an independent second look and the market price as the crowd's consensus. Reading them side by side gives more context than either alone. To see how our own projections are built, including the category-level inputs they share and the discipline behind them, read how our models work and the betting glossary.
Projections vs. odds, answered
What is a model projection?
A model projection is an independent estimate of how a specific outcome is likely to go, such as a projected stat line, a win probability, or a projected total. It combines data like performance, matchup, venue, weather, and market context. It is a forward-looking best guess expressed as a number, and it is not a report of what a book is charging.
What is a sportsbook line or price?
A sportsbook line is the price a book posts for an outcome. It reflects the book's own estimate of the probability plus a built-in margin, and it moves as bets come in and information changes. A line is as much a business decision as it is a probability estimate, because its job is to balance the money rather than only to predict the game.
Why do a projection and the line differ?
They are built for different purposes and under different pressures. A projection aims to estimate the true likelihood of an outcome, while a line has a margin baked in, shifts with betting volume, and reacts to news such as injuries, lineups, and weather. Those forces mean the two numbers rarely land in exactly the same place.
Does this apply to every sport?
Yes. An NFL spread, an NBA total, and an MLB moneyline are all priced by a book with a margin attached, and a projection can be compared to any of them the same way. The vocabulary changes from sport to sport, but the comparison between an independent estimate and a market price does not.
What does 'edge' mean here?
Edge is the gap between an independent projection and the fair price implied by the market once the book's margin is removed. When a projection rates an outcome differently than the fair line does, that difference is the edge. It measures disagreement and relative value, and it is not a signal that one side is certain to win.
What is the vig, and how does it change the picture?
The vig is the margin a book builds into its prices, which is why the two sides of a market do not add up to an even 100 percent. To compare a line to a projection fairly, you remove that margin to get a fair price, which is the market's estimate of probability without the house edge. Comparing a raw price to a projection without de-vigging would not be an apples-to-apples read.
Is a projection more reliable than the line, or the other way around?
Neither is inherently right. A projection is one independent estimate, while a sharp market price aggregates a great deal of money and information. They work best together, with the projection as a second opinion and the line as the market's consensus, rather than either being treated as the final word.
Does a projection or an edge guarantee an outcome?
No. Both a projection and a line are estimates of probability, and probability is not certainty. An edge describes long-run relative value, not the result of any single game. A projection can be wrong and a favored line can lose, so neither number is a guarantee, which is exactly why they are framed as estimates and value rather than advice.
See the two side by side
Every board puts an independent projection next to the market price and calls out the gap, so you can read the model and the line together on the day's games.