A sportsbook price is a probability with a fee hidden inside it. That is the whole idea, and most bettors never get past the first half. They know -150 means favorite and +130 means underdog, but ask them what the book is claiming about the game and they cannot say. Once you can turn a price into a percentage, and then pull the fee back out, you can tell at a glance whether a number is fair, which side is carrying the book’s margin, and whether two sportsbooks disagree enough to be worth a second account. None of it needs more than a calculator.
Turning a Price Into a Percentage
American odds answer one of two questions. A minus number says how much you risk to win $100. A plus number says how much you win on a $100 risk. Implied probability takes that same information and restates it as a share of the whole pot, which is the form your brain can actually compare.
For a minus price, divide the odds by the odds plus 100. At -150 that is 150 divided by 250, which is 60%. The book is telling you the favorite wins six games in ten.
For a plus price, divide 100 by the odds plus 100. At +130 that is 100 divided by 230, which is 43.5%. The underdog wins a little better than four in ten.
Decimal odds are quicker still: one divided by the price. A soccer side at 1.80 implies 55.6%, the draw at 3.60 implies 27.8%, and the other side at 4.50 implies 22.2%. The percentage is the same no matter how the book chooses to display the line, which is why it is the right unit for comparing prices across formats and across books.
Why the Two Sides Add Up to More Than 100
Now add the two numbers from that first game. The favorite at 60% and the underdog at 43.5% come to 103.5%. A game cannot have a 103.5% chance of ending somehow, so the extra 3.5 points is not a forecast. It is the book’s margin, built into both prices at the same time. Bettors call it the vig, the juice or the hold, and it is how a sportsbook makes money on a game it has no opinion about.
The version everyone knows is the point spread at -110 on each side. Each side implies 52.4%, together they make 104.8%, and if the money splits evenly the book keeps about 4.5% of everything bet. That 52.4% is also your break-even rate. Win 52% of your spread bets at -110 and you are losing money, which is a surprise to anyone who assumed “over 50%” was the finish line.
The three-way soccer market above adds to 105.6%. Three outcomes give the book three places to tuck margin away, which is why the draw at 3.60 is almost always a worse price than it looks.
Taking the Vig Out
To see what the book really thinks, divide each side’s implied probability by the total. That is all removing the vig is. The result is the pair of fair prices the book would post if it charged nothing.
Back to -150 and +130. The total is 103.5%. The favorite’s 60% divided by 103.5% is 58%. The underdog’s 43.5% divided by 103.5% is 42%. Those add to 100%, and they are the book’s actual opinion: the favorite wins about 58 times in a hundred. Turned back into American odds, 58% is roughly -138 and 42% is roughly +138. The bettor laying -150 is paying -150 for a side worth -138. The bettor taking +130 is getting +130 for a side worth +138. Each is paying about 12 cents of vig, and neither has found a bargain.
Try a bigger favorite, -200 against +170. Implied: 66.7% and 37%, total 103.7%. Fair: 64.3% and 35.7%, which is about -180 either way. The favorite bettor is paying 20 cents of vig for a side worth -180. The underdog bettor is paying 10. That split is not an accident. Books know where recreational money goes, and it goes on favorites, so that is where they load the margin.
This straight division is the method most bettors use, and it is plenty for sides and totals. It is a little off on long shots, because it assumes the margin is spread evenly across every outcome and books do not price that way. On a 20-team futures board the long shots carry far more than their share. If you bet futures seriously there are better methods, but for a game with two or three outcomes the simple version lands within a point or two of the truth.
Where the Hold Is Worst
Once you can work out hold, you start to notice how much it moves from one market to the next. A few things are true at every offshore sportsbook we cover.
Main lines are the cheapest thing on the board. NFL and NBA sides and totals usually sit between 104.5% and 105%, and a reduced-juice book cuts that further. SportsBetting.ag’s -105 on NFL and NBA sides implies 51.2% a side, 102.4% in total, which pulls your break-even rate from 52.4% down to 51.2%. Over a few hundred bets that is the difference between a small loser and a small winner for a lot of people.
Player props are the most expensive market bettors treat as cheap. A prop at -115 both ways implies 107%. At -120 both ways it is 109%. A bettor grinding props at those prices needs about 54.5% just to break even, and that is before the book shades the number toward the side it expects the public to take.
Parlays stack the hold. Every leg carries its own margin and the book collects on each one. Two -110 legs paying +260 look generous until you notice that two coin flips land together 25% of the time, which is fair odds of +300. The book is holding about 10% on that ticket, roughly double what it holds on either leg alone. Our parlay guide walks through the full math, and the same game parlay problem explains why correlated legs make it worse.
Futures are the worst of all. Add up every team’s implied probability on a championship board and you will usually land somewhere between 130% and 150%. The book has months to hold your money and dozens of outcomes to price, and it uses both.
What to Do With the Number
Implied probability does not pick winners. It tells you what the book believes, not whether the book is right. What it gives you is a way to test a price against your own opinion and against the price down the street.
If you think a favorite wins 65% of the time and the fair price after devigging says 58%, you have a real disagreement with the market and a reason to bet. If you think 60% and the fair price says 58%, you do not have an edge. You have an opinion, and the 12 cents of vig will eat it.
Comparing books is where the number earns its keep. Two sportsbooks posting -150 and -140 on the same favorite are claiming 60% and 58.3%, nearly two points of win probability apart, and the only work involved is looking. Devig both and the gap in fair prices is smaller than the raw numbers suggest, but it is still there, and shopping it on every bet improves a record without anyone getting better at picking games. Our line shopping guide covers how to set that up across two or three accounts.
The last use is the one that pays over years rather than weeks. Write down the fair probability of every side you bet, then compare it to the fair probability of the closing price. If your numbers keep landing on the right side of the close, you are reading the market well. That is closing line value, and implied probability is the unit it is measured in. Make the percentage the first thing you see when you look at a line instead of the last.