American Odds to Implied Probability

American odds describe a payout. Implied probability rewrites that payout as the break-even win rate built into the price. The conversion is useful because percentages are easier to compare across favorites, underdogs, and sportsbooks.

Use the Iverson Bets odds calculator if you want the answer immediately. The formulas below show where the answer comes from.

The two formulas

For negative odds, use the absolute value of the odds:

$P = \frac{|odds|}{|odds| + 100}$

For positive odds:

$P = \frac{100}{odds + 100}$

Multiply the result by 100 to express it as a percentage.

What the percentage means

A team priced at -150 has an implied probability of 60%. If you repeatedly bet that price, you need to win more than 60% of those bets to have a positive return before considering limits, voids, or other costs.

That does not mean the team has a true 60% chance to win. It means the offered price has a 60% break-even point. Sportsbooks include a margin in their prices, and different books may post different odds on the same game.

Favorite example

Suppose Boston is -180.

$P = \frac{180}{180 + 100} = 0.6429$

The implied probability is 64.29%. A $180 stake would return $280 if the bet wins: the original $180 plus $100 in profit.

Underdog example

Suppose Orlando is +155.

$P = \frac{100}{155 + 100} = 0.3922$

The implied probability is 39.22%. A $100 stake would return $255 if the bet wins: the original $100 plus $155 in profit.

Why both sides add to more than 100%

If one side is -110 and the other is also -110, each side implies 52.38%. Together they add to 104.76%, even though only one side can win.

The amount above 100% is commonly called the overround or vig. To estimate the market's no-vig probabilities, normalize both sides so they add to 100%. The next guide walks through that calculation.

Common mistakes

• Do not use the positive-odds formula for a negative number.
• Do not treat implied probability as a prediction or guarantee.
• Do not compare a model probability with only one side of a two-sided market when the sportsbook margin is still embedded.
• Do not ignore price differences. +155 and +165 describe different break-even points for the same outcome.

A practical workflow

1. Record both sides of the market and the sportsbook offering them.
2. Convert each price to implied probability.
3. Remove the vig before treating the pair as a market estimate.
4. Compare that no-vig estimate with your own documented probability.
5. Check the live price again before making a decision.

The arithmetic is the easy part. The difficult part is producing a probability estimate that remains accurate on games you have not already inspected.