Prediction Markets
Calculator
Convert any contract price into American odds, decimal odds, and implied probability: instantly. Then use the EV calculator to check if a trade has positive expected value.
Convert price โ odds โ probability
Enter any one value: the other three update instantly.
Is this trade worth making?
Enter your own probability estimate and the market price to see whether the trade has positive expected value: and how much edge you have.
Common price โ odds conversions
| Price (p) | Implied Prob. | American Odds | Decimal Odds |
|---|
The maths behind the conversions
Why a 65p contract = 65% chance
A YES share in a binary prediction market pays ยฃ1 if the event happens and ยฃ0 if it doesn't. YES + NO always sum to ~ยฃ1. So a YES share at 65p implies a 65% chance, anyone who thought the true probability were higher would buy YES and push the price up.
How the ยฑ format works
Favourite (โ): How much to stake to win ยฃ100. โ185 means stake ยฃ185 to profit ยฃ100.
Underdog (+): What you win on a ยฃ100 stake. +200 means stake ยฃ100 to profit ยฃ200.
Formula: p โฅ 50%: odds = โp/(100โp) ร 100. p < 50%: odds = (100โp)/p ร 100.
Total return per unit staked
Decimal odds represent your total return including your stake. 1.54 means you receive ยฃ1.54 for every ยฃ1.00 staked (profit of ยฃ0.54). Formula: decimal = 100 รท implied_probability. Below 2.0 = favourite; above 2.0 = underdog.
Edge = your estimate โ market price
If you think something has a 55% chance and the market prices it at 65p, you have 15 percentage points of edge. EV = stake ร (your_prob โ market_price) รท market_price. Positive EV doesn't guarantee profit on any single trade, but positive-EV trading is profitable in the long run.