1. Select the odds format
Enter decimal, fractional, American, or odds-ratio values.
Odds and probability conversion
Odds-to-Probability Calculator
Convert fractional, decimal, American, or ratio odds into implied probability. Review complementary probability, fair odds, expected counts, potential payout, bookmaker overround, and normalized no-vig probabilities.
Four odds formats
Implied probability
Margin and no-vig analysis
Implied probability
40.00%
Decimal odds
2.50
American odds
+150
Convert odds into implied probability
Choose the odds format, enter the quoted odds, and review equivalent formats and probability metrics.
Implied probability reflects the probability encoded by quoted
odds. Betting-market odds may include bookmaker margin, exchange
commission, liquidity effects, promotions, and rounding, so they
are not always the same as a fair or true probability.
How the Odds-to-Probability Calculator works
The tool first converts the selected odds format into decimal odds. It then calculates implied probability and translates the result into equivalent fractional, American, and ratio formats.
2. Calculate implied probability
The calculator converts the quoted odds into the probability encoded by those odds.
3. Review margin and value
Compare implied probability with your estimate, expected value, payout, overround, and normalized no-vig probability.
Decimal Odds to Probability
Probability = 1 ÷ Decimal Odds
Fractional Odds to Probability
Probability = Denominator ÷ (Numerator + Denominator)
American Odds to Probability
Positive: 100 ÷ (Odds + 100); Negative: |Odds| ÷ (|Odds| + 100)
| Odds format | Example | Equivalent probability | Interpretation |
|---|---|---|---|
| Decimal | 2.00 | 50.00% | Total return is twice the stake if successful. |
| Fractional | 3/2 | 40.00% | Profit of 3 units for every 2 units staked. |
| American positive | +150 | 40.00% | Profit of 150 units from a 100-unit stake. |
| American negative | -200 | 66.67% | Stake 200 units to earn 100 units of profit. |
| Odds in favour | 2:3 | 40.00% | Two expected successes for every three failures. |
Frequently asked questions
Important details for converting odds and interpreting implied probability.
What is implied probability?
Implied probability is the chance represented by quoted odds before adjusting for bookmaker margin or personal estimates.
How do decimal odds convert to probability?
Divide 1 by the decimal odds, then multiply by 100 to express the result as a percentage.
How do fractional odds convert to probability?
Divide the denominator by the sum of the numerator and denominator.
How do positive American odds work?
Positive American odds show the profit from a 100-unit stake. For example, +150 means 150 units of profit from 100 units staked.
How do negative American odds work?
Negative American odds show the stake required to earn 100 units of profit. For example, -200 means staking 200 units to earn 100 units.
What is bookmaker overround?
Overround is the amount by which all quoted implied probabilities exceed 100%. It is a common measure of the built-in market margin.
What are no-vig probabilities?
No-vig probabilities normalize all market probabilities so they total exactly 100%, removing the proportional overround.
Does implied probability equal the true probability?
Not necessarily. Quoted odds may include margin, commission, promotions, rounding, liquidity effects, and market opinion.