Implied Probability Calculator

An implied probability calculator turns any American or decimal moneyline into the win chance the sportsbook is actually pricing, then adds both sides of an NFL, NBA, MLB, or NHL market together to reveal the vig baked into the number.

What Is Implied Probability?

Implied probability is the win chance hidden inside a price. Every set of odds is a bet the book is offering, and if you flip it around, it tells you the probability the book is charging you for. A moneyline of -150 implies a 60% chance; +150 implies 40%. Sportsbooks start from a probability estimate and convert it into a price, and bettors can reverse the process to see what the book actually believes.

The catch is that on a two-way market, the two implied numbers add up to more than 100%. That overround is the book’s built-in margin, the vig, and it exists on essentially every line at a US sportsbook, whether it’s an NFL spread, an NBA moneyline, or an MLB run line. A market that showed exactly 100% between its two sides would be a fair, vig-free market, but no book actually offers one, because the margin is how the book gets paid for taking the bet.

Knowing the implied probability is the first step to judging whether a price is generous or a trap. On its own, a single number doesn’t tell you much; the real value comes from comparing it with your own estimate of the true chance a team wins, and from stripping the vig out so you’re comparing against a fair number instead of an inflated one.

How Implied Probability Is Calculated

The formula depends on which side of the line you’re reading. For a favorite, priced with negative American odds, implied probability equals the absolute value of the odds divided by the absolute value of the odds plus 100. A -150 favorite works out to 150 divided by 250, which is 60.0%. For an underdog, priced with positive American odds, implied probability equals 100 divided by the odds plus 100. A +130 underdog works out to 100 divided by 230, which is 43.5%.

If you’re starting from decimal odds instead, the math is simpler: implied probability is just 1 divided by the decimal price. A decimal price of 1.67, which is the decimal equivalent of -150, gives 1 divided by 1.67, landing back on that same 60.0%. A decimal price of 2.50, the equivalent of +150, gives 1 divided by 2.50, or exactly 40.0%. Both routes land on the same implied percentage, since American and decimal odds are just two notations for the same price.

Once you have both sides of a two-way market converted to percentages, add them together. That sum is always going to land above 100% at a real sportsbook. Subtract 100% from the total and what’s left is the vig. This step matters because neither side’s number by itself tells you the size of the book’s margin — only the combined total does.

What the Calculator Shows You

The calculator produces a small set of numbers for each price you enter. First, the implied win probability for a single side, expressed as a percentage, so you can see at a glance what chance of winning a given American or decimal price is asking you to accept. Second, when you enter both sides of a two-way market, it shows the market total, the sum of the two implied probabilities. Third, it shows the vig, the amount that total exceeds 100%, which is the sportsbook’s built-in margin on that market. Together these outputs move you from a raw price to a percentage you can reason about, and from a single percentage to a view of how much the book is charging you to take either side of the bet.

Worked Example

Take a two-way NFL moneyline priced -150 on the favorite and +130 on the underdog. Start with the favorite. Since -150 is a negative American price, the formula is the absolute value of the odds divided by the absolute value of the odds plus 100: 150 divided by 250. That comes out to a 60.0% implied probability. In other words, the -150 price is asking you to accept that the favorite wins 60.0% of the time.

Now do the underdog. Since +130 is a positive American price, the formula is 100 divided by the odds plus 100: 100 divided by 230. That comes out to a 43.5% implied probability, meaning the +130 price is asking you to accept a 43.5% chance the underdog wins.

Add the two together: 60.0% plus 43.5% equals a market total of 103.5%. Since a fair, vig-free market would have both sides add up to exactly 100%, the extra amount above that, 3.5%, is the vig, the sportsbook’s built-in margin on this particular moneyline.

That 3.5% is not charged to one side or the other; it’s spread across the whole market. The book has inflated both implied chances above what it actually believes, so it keeps that margin no matter which side the public bets. Once you see the market total sitting at 103.5% rather than 100%, this moneyline is running a fairly tight 3.5% vig, and that number becomes the benchmark you compare against other moneylines, or against your own estimate of each team’s real chances.

Implied Probability by American Price

Here’s how implied probability moves as an American price gets shorter or longer. Shorter, more negative prices like -200 imply a bigger favorite and a higher win chance, while longer, more positive prices like +200 imply a bigger underdog and a lower win chance. The decimal equivalent is included alongside each American price so you can cross-check either notation.

Favorite and Underdog Implied Chances on Common Two-Way Lines

This table pairs a favorite price with its matching underdog price on three common two-way lines, so you can see both implied percentages and the resulting vig side by side. Notice that the vig isn’t fixed: a pick’em-style -110/-110 line carries a noticeably higher vig than a -150/+130 line, even though both are ordinary two-way markets.

The Vig Is in the Sum, Not Either Side

The number to watch is the sum, not either side on its own. A single -110 implies 52.4%, and two of them on a spread add to 104.8%, so the standard -110/-110 market carries a 4.8% vig. Sharper books trim that to nearer 2%; recreational books stretch it wider. Looking at just one side of a -110/-110 line tells you nothing about how much margin the book is taking, because 52.4% looks the same whether the other side is also -110 or something looser.

A second subtlety is that the raw implied probabilities are not true probabilities. They include the vig, so both sides are inflated above what the book actually believes. To recover the book’s real estimate, you would strip the vig out proportionally, which lowers both numbers so they sum to exactly 100%. That vig-free figure, not the raw implied number, is what you should compare against your own read of the game.

This distinction matters most at the margins: whenever your own estimate clears the vig-free implied number, rather than just the raw one, the price has value. Comparing your estimate to the raw number instead makes every price look tougher to beat, since that number still carries the book’s margin. Separating the two turns a simple odds conversion into a genuine edge-finding step.

When Implied Probability Makes Sense

Implied probability is most useful as a first filter, not a final verdict. Converting a moneyline to a percentage gives you a common language to compare prices across games and sports, whether it’s an NFL spread, an NBA total, or an MLB run line, and it’s the fastest way to see how big a favorite or underdog a price treats a team as, without doing the arithmetic in your head.

Where it makes the most sense is as a bankroll and value check before you place a bet. If your own honest estimate of a team’s chances is higher than the vig-free implied probability, the price may be offering value; if your estimate is lower, the price is likely overpriced for that side. Because the raw number always includes the vig, work from the vig-free figure when deciding whether a line is worth betting, and treat the raw percentage as a starting point rather than a final answer.

It’s less useful in isolation, without a view of your own. Implied probability only tells you what the book is charging for; it does not tell you what will actually happen in the game. Bettors who rely on the implied number alone, without an independent read on the matchup, are really just betting according to the book’s own margin-inclusive view. And because the vig varies from market to market, the same raw price can represent different amounts of real value depending on where you’re looking.

Common Mistakes

Treating the raw implied percentage as the true chance is the most common error, since it still includes the vig. A related mistake is forgetting to add both sides together, the only way to see the market’s total margin rather than one side in isolation. Bettors also often compare their own estimate directly to the raw implied number instead of the vig-free one, which understates the value of a good price. Finally, it’s easy to assume a low-vig market and a high-vig market offer the same value at an identical price, when the size of the vig actually changes how much room there is for a bet to be worth making.

Implied Probability vs. Vig-Free Probability

Raw implied probability includes the sportsbook’s margin; vig-free probability strips that margin out proportionally so both sides sum to exactly 100%. On a -150 / +130 market, the difference shows up clearly once the vig is removed.