Reverse the odds calculation
This tool starts with a probability rather than a quoted price. An estimated 55% chance implies decimal odds of 1 ÷ 0.55 = 1.81818, equivalent to about −122.22 in American odds. That is the theoretical zero-EV price for a win/loss bet if the estimate is accurate, before fees or other adjustments.
Compare the offered price in the right direction
A higher decimal price pays more for the same stake. At a 55% estimate, −110 (decimal 1.90909) offers a higher payout than break-even, while −130 (decimal 1.76923) offers a lower payout. Negative American odds can make the comparison unintuitive; converting both prices to decimal can make it clearer.
An estimate is not a safety margin
At 52% the break-even decimal price is about 1.923; at 58% it is about 1.724. That spread shows how sensitive a fair price is to the underlying probability. Rounding to a whole American price can also obscure a very small difference. Compare unrounded values when the decision is close.
When the simple conversion applies
The conversion assumes a binary win/loss outcome. If the market can push and refund the stake, use the chance of winning conditional on a non-push when applying this simple conversion. Markets with a draw, partial payout or dead-heat reduction require an outcome-specific calculation. Use the EV calculator to understand how payout and a probability estimate combine.
Examples are hypothetical and rounded. These calculators explain arithmetic; they do not establish a model’s accuracy or guarantee an outcome.