How the prediction markets converter calculator works
Prediction markets such as Kalshi and Polymarket quote a share price between 0 and 1 that pays 1 if the event happens. That price is a probability, so it converts directly into betting odds and can be compared with a bookmaker's price on the same event.
- The share price is the implied probability: 0.65 means 65%.
- Decimal odds are 1 divided by the price.
- American and fractional odds follow from the decimal price as usual.
Worked example
A share trading at $0.65.
- Probability 65%, decimal odds 1.54, American −186.
- A bookmaker offering 1.70 on the same outcome is paying more than the market thinks it is worth.
Prediction-market prices carry a spread rather than a margin: the buy and sell prices differ, so use the price you can actually trade at.
Questions
- Is a prediction market price the same as a bookmaker's odds?
- It is a probability with a bid-ask spread instead of a margin. Convert it to odds and it is directly comparable, as long as you use the executable price.
- Why enter the price as a decimal between 0 and 1?
- Because that is how the contracts are quoted: a $0.65 share pays $1.00 if the event resolves yes. If you enter 65 the calculator reads it as cents.
- Can I arbitrage a prediction market against a bookmaker?
- The arithmetic is the same as any two-way arbitrage. The practical limits are liquidity, fees and settlement rules, which differ between the two.
