Implied Probability: A Price Is Not a Prediction

The universal formula

First convert the price to decimal odds D, then calculate implied probability = 100 ÷ D. Decimal 2.50 gives 40%; decimal 1.50 gives about 66.67%; decimal 4.00 gives 25%.

At +150, winning 40 of 100 identical $100 bets would return $10,000 in total against $10,000 staked. This is a mathematical illustration, not a forecast of how any set of bets will perform.

American shortcuts

For positive American odds A, probability = 100 ÷ (A + 100). For negative odds A, probability = |A| ÷ (|A| + 100). Multiply by 100 to display a percentage.

At −110 the calculation is 110 ÷ 210 ≈ 52.38%. At +200 it is 100 ÷ 300 ≈ 33.33%. Rounding these percentages before using them in other formulas can introduce small discrepancies.

Why a market can add to more than 100%

Suppose two opposing outcomes are both −110. Each implies about 52.38%, giving a combined 104.76%. The excess of about 4.76 percentage points is the market’s quoted margin above 100%.

Divide each raw implied probability by the sum to normalize the pair proportionally. Here that gives 50% per side and fair decimal odds of 2.00. This is one no-vig estimation method, not evidence that the real chances are equal.

An independent estimate changes the question

If you estimate a 45% chance at decimal 2.50, theoretical expected return is 0.45 × 2.50 − 1 = 12.5% of stake. If your estimate is wrong, that apparent edge can disappear.

The bookmaker’s price may reflect its margin, liabilities and market information. Do not confuse a precise numerical conversion with certainty about a sporting event.

Explore the numbers

Use the calculators to try these examples with your own inputs. Calculations describe prices and conditional returns, not guaranteed outcomes.

Convert odds and calculate payout

Estimate fair odds from probability

Calculate expected value

Explore two-way sportsbook margin