Implied Probability in Betting: How to Calculate It From Any Odds

Implied probability is the chance of a result happening according to the betting odds, written as a percentage. It turns any price into a number you can compare: -110 odds imply a 52.4% chance, +150 implies 40%, and -200 implies 66.7%. Knowing how to calculate implied probability is the quickest way for a bettor to judge whether a bet is worth making.

This guide covers the implied probability formula for American, decimal and fractional odds, why the percentages add up to more than 100%, how to remove the bookmaker's margin, and how to use the numbers to find value bets.

Understanding implied probability

Every betting price is really a probability in disguise, and implied probability in sports betting is simply that probability written out. When a sportsbook lists a team at -150 on the moneyline, it's saying that team wins about 60% of the time, before its margin. Once you convert odds into implied probabilities, you can check each bet before placing it: is your estimate of the likelihood of winning higher than the price implies?

If you think a team wins 50% of the time and the odds imply 40%, the bet has value. If the odds imply 60%, it has none, however much you like the team.

How to convert American odds to implied probability

American odds use two formulas, one for negative numbers (favorites) and one for positive numbers (underdogs):

• Negative odds: odds ÷ (odds + 100). For -150: 150 ÷ 250 = 0.60, or 60%.
• Positive odds: 100 ÷ (odds + 100). For +150: 100 ÷ 250 = 0.40, or 40%.

Use the number without its minus sign in the formula. Here are some common prices:

New to the minus and plus signs? Our guide on how to read American odds explains them first.

Implied probability in other odds formats

Decimal odds are the easiest: divide 1 by the decimal price. Odds of 2.50 imply 1 ÷ 2.50 = 40%. Odds of 1.50 imply 66.7%, and 1.91 (about -110) implies 52.4%. To convert between formats, see our guide to converting decimal odds to American odds.

For fractional odds, divide the second number by the sum of both numbers. At 3/2, that's 2 ÷ (3 + 2) = 40%. At 5/1, it's 1 ÷ 6 = 16.7%. The three formats give the same answer for the same price: +150, 2.50 and 3/2 all imply 40%.

Why the percentages add up to more than 100%

Add up the implied probability of every outcome in a market and you'll get more than 100%. Take a game with both teams at -110: each side implies 52.4%, for a total of 104.8%. The extra 4.8% is the overround, the sportsbook's margin, also called the vig or juice. It's how the bookmaker makes money no matter who wins.

Bigger overrounds mean worse prices for bettors, and sportsbooks don't all use the same margin. A market adding up to 103% is better for you than one adding up to 108%.

How to remove the vig and find the fair odds

To estimate the true probability the sportsbook has in mind, take out its margin. Divide each side's implied probability by the total:

1. Ravens -150 implies 60.0%, and Steelers +130 implies 43.5%.
2. Together they add up to 103.5%.
3. Ravens: 60.0 ÷ 103.5 = 58.0%. Steelers: 43.5 ÷ 103.5 = 42.0%.

Those no-vig numbers add up to 100% and are the market's fair estimate of each team's chance of winning. This is the starting point many sharp bettors use before deciding whether a price is off.

Using implied probability to find value bets

A value bet is one where your estimate of the true chance is higher than the implied probability: the price is mispriced in your favor. Here's how it plays out over time with a $100 bet at +150 (40% implied) on a team you think wins 45% of the time:

• 45% of the time you win $150: 0.45 × 150 = $67.50.
• 55% of the time you lose $100: 0.55 × 100 = $55.00.
• Expected value: $67.50 − $55.00 = +$12.50 per bet.

That's positive expected value. Any single bet can still lose, but bets like this pay off over many tries if your 45% estimate is right, and getting the estimate right is the difficult part.

Break-even win rates

Implied probability is also your break-even point. At -110, you need to win 52.4% of your bets to break even, not 50%, because of the vig. Our article on what -110 means in betting shows the math. At +150 you only need to win 40% of the time, but those bets lose more often.

Implied probability for parlays

For a parlay, multiply the implied probability of each leg. Two legs at -110 each: 0.524 × 0.524 = 27.4%. Three legs: about 14.4%. The odds pay more as you add legs, but the chance of winning drops fast, and the sportsbook's margin is stacked on every leg. See how to calculate a parlay payout for the payout side.

Common mistakes

• Forgetting the vig. A team at -110 isn't a 50% bet; you need 52.4% to break even.
• Treating a big underdog as value. +400 pays well, but it implies 20%. It's only value if the real chance is higher.
• Using the minus sign in the formula. Use 150, not -150, for odds ÷ (odds + 100).
• Mixing up the format. 2.50 in decimal format is not the same price as +250 in American odds. An implied probability calculator saves time, but the formulas above are all you need.

Try it on Paid2Bet

Practice reading odds as probabilities with a free balance on Paid2Bet. Open the Bet page, pick a game, and work out what each price implies before you tap it. The bet slip shows what you'd win, so you can check your math. For more on how odds work, start with our guide on how betting odds work.

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