How this calculator works
Decimal odds quote the full return including the original stake. Fractional odds quote profit relative to stake. Positive American odds quote profit on 100 units; negative American odds quote the stake needed to profit by 100 units. Their reciprocal decimal price gives the break-even probability before fees. Bookmaker margins mean probabilities across all mutually exclusive outcomes can sum above 100%. A quoted price alone does not establish the true event probability.
Formula
Implied probability = 1/D. Fractional a/b gives D = 1 + a/b. American A > 0 gives D = 1 + A/100; A < 0 gives D = 1 + 100/|A|.
Worked example
Decimal odds 2.5 imply 1/2.5 = 40%. American odds -200 mean risking 200 to profit 100, equivalent to decimal 1.5 and implied probability 66.67%.
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Frequently asked questions
Do decimal odds include the stake?
Yes. At decimal odds 2.5, a winning $10 stake returns $25 in total, including $15 profit.
Do these probabilities remove the bookmaker margin?
No. They convert each quoted price directly. Removing margin needs prices for the entire outcome market and a stated adjustment method.
What does probability 100% produce?
It gives decimal odds of one and zero profit. No finite American quote represents that endpoint.