Probability calculator
Turn probabilities into prices and back, see what a price demands of you, and find out what a multiple is really worth.
Probability and price
A price and its break-even probability are the same number read from opposite sides.
Parlay
Results
Parlay
52.36% × 47.62% = 24.93%
Legs multiply, and so does the bookmaker's cut. A four-fold at 1.80 needs a 9.5% event to land.
Probability first, price second
Every price is a claim about probability, and the conversion is one division: 40% is a price of 2.50, and 2.50 is a probability of 40%. Doing that conversion before betting changes the question from "do I like this bet?" to "does this happen more than 40% of the time?" — a question you can actually be wrong about. Read from the price side, the same number is the break-even probability: the minimum chance an outcome needs for the bet to be neutral. 1.75 demands 57.1%; 1.50 demands 66.7%; 15.00 asks for only 6.7%, which is why long shots feel cheap and why books load their margin there.
Multiples are where probability turns counter-intuitive. Independent legs multiply: three bets you rate at 50% each combine to 12.5%, not to something reassuringly near a half. Four legs at 60% come to 12.96%. The combined price multiplies the same way, and that is the trap — the number gets big while the chance gets small, and the margin compounds with it. Hold on to the assumption underneath: this multiplies, so it assumes the legs are independent. Two outcomes from the same match are correlated, and there the real probability is different — usually higher than the product.
What a four-leg accumulator really costs
- Four legs at
- 1.80 each · 55.56%
- Combined price
- 10.50
- Combined probability
- 9.53%
- Margin per leg
- 5%
- Margin on the parlay
- 21.6%
The price looks generous until you notice what it demands: a 9.5% event. And the book's cut compounded four times — 1.05⁴ − 1 = 21.6% — so the same four selections cost you four times the margin of a single bet. Correlated legs from one match are a different animal: multiplying understates them, which is exactly why books price same-game multiples separately.
Questions
What is break-even probability?
The chance an outcome must have for a bet at that price to be neutral in the long run. It equals 1 divided by the decimal price, and it is the bar your own estimate has to clear before the bet makes sense.
Why is my parlay probability so low?
Because probabilities multiply. Each leg you add makes the whole bet less likely, and a chain of plausible legs quickly becomes an unlikely bet. The price rises to match, but so does the accumulated margin.
Does this work for same-game multiples?
Not exactly. Multiplying assumes the legs are independent, and outcomes inside one match usually are not. For correlated legs the real probability is different — often higher than the product — which is why books price those markets separately.
Is the implied probability of a price the true probability?
No. It still contains the bookmaker's margin, so it is systematically higher than the market's honest estimate. Use the margin calculator to strip it out before comparing with your own number.
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