Implied Probability Calculator: What the Odds Really Say

Every price is a probability in disguise. A -150 favorite tells you the sportsbook rates that side at 60%, before its margin. This implied probability calculator converts any odds into a percentage and measures the vig built into a market. It then gives you the fair, no-vig price to compare with your own view.

Implied probability formulas

• Negative American odds: |odds| ÷ (|odds| + 100)
• Positive American odds: 100 ÷ (odds + 100)
• Decimal odds: 1 ÷ decimal
• Fractional odds (a/b): b ÷ (a + b)
• Prediction market contract: price in dollars, so 62 cents = 62%

Measuring the vig

Add the implied probabilities of every outcome. The amount over 100% is the overround. The sportsbook’s hold, its expected profit per dollar wagered on a balanced market, is 1 − (1 ÷ overround).

Removing the vig

The simplest method divides each side’s implied probability by the total. That is the proportional, or multiplicative, method most no-vig calculators use.

Worked example: -150 vs +130

An NBA game is priced at -150 for the favorite and +130 for the underdog.

• Favorite: 150 ÷ 250 = 60.00%
• Underdog: 100 ÷ 230 = 43.48%
• Total: 103.48%, an overround of 3.48 points
• Hold: 1 − (1 ÷ 1.0348) = 3.36%

Removing the vig:

• Favorite fair probability: 60.00 ÷ 103.48 = 57.98%, or about -138
• Underdog fair probability: 43.48 ÷ 103.48 = 42.02%, or about +138

If your model gives the underdog a 46% chance, you are about four points above the market’s fair price. Check it in our expected value calculator.

Break-even win rates by price

When to use implied probability

• Comparing sportsbooks: a lower total overround means a fairer market. Shopping lines across books is the easiest edge there is.
• Judging tipsters and AI picks: a 55% hit rate is good at -110 and terrible at -200. Our guide to AI prediction sites explains how to judge their records.
• Prediction markets: a Kalshi contract at 30 cents and a sportsbook at +233 imply the same chance. Fees decide which is better. See our Kalshi review.
• Staking: the fair probability feeds directly into the Kelly criterion calculator.

Why sharp bettors think in percentages

Odds formats hide how close two prices really are. The gap between -110 and -105 looks trivial, yet it moves your break-even rate from 52.4% to 51.2%. Over a season of bets, that difference alone can separate a winning record from a losing one. Converting everything to percentages makes those small edges visible.

Common implied probability mistakes

• Treating the raw number as fair. The implied probability of a single price includes the book’s margin. Only the no-vig number is a fair estimate.
• Ignoring multi-way markets. Soccer 1X2, futures and racing have three or more outcomes. Add every outcome’s probability to find the true overround, which is often much higher than in a two-way market.
• Comparing across books without converting. Two sportsbooks can show different-looking prices with very different margins. Converting both to probabilities makes the cheaper market obvious.
• Forgetting that favorites carry margin too. The vig is not only on the underdog. It is spread across every side of the market.

See all our free betting calculators.

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