What is implied probability in betting?

Implied probability is the chance of an outcome that a price suggests. It is 1 divided by the decimal odds, so odds of 2.50 (+150) imply a 40% chance.

How do you calculate implied probability from American odds?

For negative odds, divide the odds by the odds plus 100: -150 is 150 ÷ 250 = 60%. For positive odds, divide 100 by the odds plus 100: +130 is 100 ÷ 230 = 43.5%.

What is the vig or bookmaker margin?

The vig, juice or margin is the sportsbook’s built-in edge. Add up the implied probabilities of every outcome in a market; anything over 100% is the margin. Two sides at -110 add up to 104.8%, a margin of about 4.5%.

What are no-vig or fair odds?

Fair odds are the prices with the margin removed. Divide each outcome’s implied probability by the total of all of them so they add up to exactly 100%, then convert back to odds. Two sides at -110 are each a fair +100.

Does implied probability tell me the real chance of winning?

Not exactly. It tells you what the price assumes. Removing the margin gets closer to the market’s view, but no price knows the true chance for certain.

Implied probability calculator

See the chance a price implies. Add both sides of the market (or a draw) to measure the bookmaker’s margin and get fair, no-vig odds.

Market2-way market

Bookmaker margin

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Outcome	Implied	Fair	Fair odds

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What implied probability means

Every price is a prediction. Odds of 2.50 say the outcome happens about 40% of the time; 1.50 says about 67%. Implied probability turns the price back into that chance:

implied chance = 1 ÷ decimal odds

With American odds: for a favorite, odds ÷ (odds + 100), so -150 is 150 ÷ 250 = 60%. For an underdog, 100 ÷ (odds + 100), so +130 is 100 ÷ 230 = 43.5%.

Finding the bookmaker’s margin

Add up the implied chances for every outcome in a market. In a fair market they would total exactly 100%. Sportsbooks price in an edge, so they always come out higher. In the example above, 60% + 43.5% = 103.5%: the extra 3.5% is the overround, and the margin is that extra as a share of the total, about 3.4%.

margin = (total implied − 1) ÷ total implied

Removing the vig: fair odds

To strip the margin out, divide each outcome’s implied chance by the total. 60% ÷ 103.5% = 58.0% and 43.5% ÷ 103.5% = 42.0%. Those fair chances add to 100%, and converting them back gives the no-vig prices of about -138 and +138.

This is the simplest, most common method, and it spreads the margin evenly across outcomes. Bookmakers often load more of it onto longshots, so treat fair odds as a close estimate rather than the exact truth.

Why it matters

If you think a team wins more often than its fair chance, the price looks good. If you think less, it does not. Even the crowd’s favorite picks only win about half the time (see the Crowd Report), so the price matters. It is the quickest way to compare your read with the market, and it is why parlays get hard so fast: the margin is paid on every leg.