Calculate odds with statistical precision, sample distributions, and inference data.
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Odds For = p / (1 - p) = a : b, p = a / (a + b), EV = (p · Win) - ((1 - p) · Stake)pOdds (a : b)Decimal Odds (D)American Odds (+/-)EV“Evaluating an event offering 4 to 1 odds against an occurrence with a $100 stake.”
Divide favorable possibilities by total possibilities (favorable + unfavorable).
Total return per dollar risked equals 1 (stake returned) plus 4 (profit).
Since the profit on a $100 stake is $400, the American format is +400.
At mathematically fair odds, long-run expected monetary value equals zero.
A 4:1 underdog has a 20% win chance. Risking $100 yields $400 in net profit or $500 in total return upon success.
| Probability | Fractional Odds | Decimal Odds | American Odds | Break-Even Win Rate |
|---|---|---|---|---|
| 10.0% | 9/1 | 10.00 | +900 | 1 in 10 |
| 20.0% | 4/1 | 5.00 | +400 | 1 in 5 |
| 33.3% | 2/1 | 3.00 | +200 | 1 in 3 |
| 50.0% | 1/1 (Evens) | 2.00 | +100 | 1 in 2 |
| 66.7% | 1/2 | 1.50 | -200 | 2 in 3 |
| 80.0% | 1/4 | 1.25 | -400 | 4 in 5 |
| 90.0% | 1/9 | 1.11 | -900 | 9 in 10 |
Provide your numeric inputs into the designated fields in Odds Calculator.
Observe real-time recalculations as values update without requiring a manual submit button.
Click 'Copy' to copy formatted results, or use 'Share Link' to bookmark your exact configuration.
Divide 1 by the decimal odds. For example, decimal odds of 2.50 convert to 1 / 2.50 = 0.40 or 40.0% implied probability.
Positive odds (+150) indicate the net profit earned on a $100 bet ($150 profit). Negative odds (-150) indicate the amount you must risk to win $100 in net profit ($150 staked wins $100).
Expected Value measures the average outcome per bet if repeated thousands of times. A positive EV (+EV) indicates a mathematically profitable wager long-term, while negative EV (-EV) guarantees losses over time.
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