Probability to Odds Calculator
Odds are the flip side of probability: fair decimal odds equal 100 divided by the probability in per cent. 50% is 2.00, 80% is 1.25, 25% is 4.00. A bookmaker prices below the fair figure because it builds a margin into the market, so the calculator shows both values.
You can work out a single outcome, a two-way market, a football 1X2 market, or the odds behind a known stake and return. It does not predict anything: the result is only as accurate as your estimate of the chance.
Convert probability to odds
Enter probability as a percentage: 50 means 50%. Fractions work too: 0.5 means 50%. For two and three outcomes the calculator scales the total to 100% if your figures do not add up.
Inputs
Results update automatically. Decimals can use a point or a comma, and thousands separators are accepted. Values below 1 are read as fractions, values from 1 upwards as percentages: 1 means 1%, not 100%.
Result
Fill in the fields and the result will appear automatically.
How bookmakers turn a probability into odds
A price on the board comes from three steps: estimate the probability of the outcome, convert it into fair odds, then cut those odds by the margin.
Fair odds = 100 / probability (%)Odds with margin ≈ fair odds / (1 + margin)Several outcomes: outcome probability / total of probabilities × 100%Odds from the return = return / stakeThe margin goes in as a fraction: 5% is 0.05. The higher the probability, the lower the fair odds, and vice versa: an event with a 10% chance has fair odds of 10.00, one with a 90% chance has 1.11.
The margin shows up in the total of the probabilities. In a fair market the outcomes add up to exactly 100%; in a real one they add up to more. With a 5% margin the implied probabilities of a 1X2 market total 105%. If money comes in proportionally across the outcomes, the bookmaker's theoretical take is 5 / 105 = 4.76% of turnover, which is also what a bettor loses on average per bet at those prices.
Probability to odds conversion table
Ready-made values for common probabilities. Odds with margin assume a 5% margin applied by the proportional rule.
| Probability | Fair odds | With 5% margin |
|---|---|---|
| 95% | 1.05 | 1.00 |
| 90% | 1.11 | 1.06 |
| 80% | 1.25 | 1.19 |
| 75% | 1.33 | 1.27 |
| 70% | 1.43 | 1.36 |
| 66% | 1.52 | 1.44 |
| 60% | 1.67 | 1.59 |
| 55% | 1.82 | 1.73 |
| 51% | 1.96 | 1.87 |
| 50% | 2.00 | 1.90 |
| 45% | 2.22 | 2.12 |
| 40% | 2.50 | 2.38 |
| 33% | 3.03 | 2.89 |
| 30% | 3.33 | 3.17 |
| 25% | 4.00 | 3.81 |
| 20% | 5.00 | 4.76 |
| 15% | 6.67 | 6.35 |
| 10% | 10.00 | 9.52 |
| 5% | 20.00 | 19.05 |
| 4% | 25.00 | 23.81 |
| 1% | 100.00 | 95.24 |
The top row shows where the proportional rule breaks down: at a 95% chance and a 5% margin the odds fall to 1.00, so the bet no longer makes sense. In practice bookmakers take a smaller margin on outcomes like this or do not offer the market.
Example: a 1X2 market from your own estimate
Say you rate the home win at 45%, the draw at 28% and the away win at 27%.
| Outcome | Your probability | Fair odds | With 5% margin |
|---|---|---|---|
| Home (1) | 45% | 2.22 | 2.12 |
| Draw (X) | 28% | 3.57 | 3.40 |
| Away (2) | 27% | 3.70 | 3.53 |
If the bookmaker offers 2.30 on the home win, that is above the fair price by your estimate: the expected return is 2.30 × 0.45 = 1.035, or plus 3.50% per unit staked. That edge exists only inside your estimate, though. Being 3 points out, 42% instead of 45%, turns it into minus 3.40%. Before backing a price like this, run it through an expected value check that shows how sensitive the edge is to your estimate.
Odds from the stake and the return
When you know the stake and the return, the odds come straight from division: return / stake. A 100 stake returning 250 means odds of 2.50. If you only know the net profit, add the stake back first: a profit of 150 on a 100 stake is the same 250 return and the same 2.50 odds.
This is a quick way to check what odds a winning single or accumulator was settled at when your bet history only shows the amount. A return smaller than the stake is no longer a win at odds but a partial refund or an early cash out, which needs a cash out calculation instead.
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Frequently asked questions
What odds match an 80% probability?
Fair odds are 1.25 (100 / 80); with a 5% margin, about 1.19. For 90% it is 1.11 and 1.06, for 66% it is 1.52 and 1.44, for 33% it is 3.03 and 2.89. The other values are in the table above.
What odds is a 1 in 25 chance?
It depends on how it is written. "One in 25" is a 4% probability and fair odds of 25.00: the N in "1 in N" is the fair decimal price. Fractional odds of 25/1 mean winning 25 for every unit staked, on top of the stake: decimal odds of 26.00 and a probability of 3.85%.
How does a bookmaker calculate odds?
It estimates the probability of the outcome, converts it into fair odds and cuts them by the margin. After that the price moves with betting volume and news, so the final odds are not just an estimate of the chance but also the price at which the bookmaker is willing to take money on that outcome.
How do I work out the odds from the winnings?
Divide the return by the stake: 250 / 100 = 2.50. If you only know the profit, add the stake and divide by the stake: (150 + 100) / 100 = 2.50. The calculator has a separate mode for this.
Can I enter a probability as 0.5?
Yes. Values below 1 are read as fractions, so 0.5 means 50%. Values from 1 upwards count as percentages: 1 means 1%, not 100%.
Why are the odds with margin lower than the fair odds?
The bookmaker builds its edge into the market: the probabilities of all outcomes add up to more than 100%, and every price ends up below fair. With a 5% margin, fair odds of 2.00 become roughly 1.90.
Will the calculator give me an accurate prediction?
No. It only converts a probability into odds. The accuracy of the result depends entirely on how well the probability is estimated: an error of 3 percentage points around a 45% chance shifts the fair odds by 7.14%, which is more than a typical bookmaker margin.