Calculator
American Odds Converter
Convert American odds to decimal and fractional odds, implied probability, and the price-based break-even win rate.
Formula used
Positive implied probability = 100 / (odds + 100). Negative implied probability = absolute odds / (absolute odds + 100).
Worked example
-150 converts to 1.67 decimal odds, 2/3 fractional odds, and a 60.00% break-even probability before removing market margin.
When this calculator helps
Use this converter to compare positive and negative American prices on a common decimal, fractional, and implied-probability scale. It is especially helpful before calculating break-even rate, no-vig probability, CLV, or a risk-to-win amount.
The output describes the entered price. It does not estimate the underlying team strength or determine whether the price is fair.
Understanding the result
The implied probability is also the long-run break-even win percentage before other costs under a constant-price, constant-risk model. It is not automatically a fair probability because a quoted market can include margin.
Decimal odds include the returned stake. Implied probability translates the quoted return into the win rate that breaks even before other assumptions under constant price and risk. Positive American odds imply a lower break-even rate than an equally sized negative number.
If opposing implied probabilities total above 100%, the market contains quoted margin. Use a complete-market normalization before calling either side a no-vig estimate.
Before relying on the output
- Valid American odds outside the invalid -99 through +99 range
- No early rounding in follow-up calculations
- Implied probability not mislabeled as fair probability
Common mistakes
- Reading -150 as a 150% probability.
- Calling implied probability no-vig probability without using the other market outcomes.
- Rounding too early when comparing prices.
Limitations
- The conversion reflects the entered price only.
- Fractional output is reduced from the exact American-price ratio.
- Market margin and push probability require additional context.
Frequently asked questions
Is implied probability the same as fair probability?
Not necessarily. A quoted price can include sportsbook margin; no-vig normalization requires the complete market.
What is break-even win rate?
It is the win percentage that produces zero expected return at the entered price under the stated assumptions.
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