American NBA odds and implied probability

Positive and negative prices use different fractions

For positive American odds of +120, divide 100 by 120 plus 100. The result is 45.45% after rounding. For negative odds of −110, divide 110 by 110 plus 100 to get 52.38%. These are implied percentages for the quoted prices.

The sign does not indicate the direction of a point spread. +120 is a price; +4.5 is a spread. A screen can show both on the same selection, so label them separately.

Implied is not fair probability

The two sides of a sportsbook market commonly sum to more than 100% after conversion. That excess is the quoted overround. A single price's implied percentage is therefore not automatically an unbiased estimate of the outcome's chance.

If you compare sportsbooks, match the exact event, market, selection and spread or total line first. A more favourable payout at the same line implies a lower break-even percentage, but it does not by itself prove an edge over the true chance of winning.

Use the conversion for a decision, not a prediction

The arithmetic helps interpret price. It does not supply an NBA model, lineup assessment or expected value. Confirm the game on the official schedule and the current price at a sportsbook serving your location before relying on a quote.

• For +A, calculate 100/(A+100).
• For −A, calculate A/(A+100), using A as a positive magnitude.
• Do not call the result a fair probability without addressing margin.