Three unmarked odds tickets beside generic counters and a simple calculator. Original AI-generated artwork produced for GreenCalc; not a measured diagram or empirical data display.
Define profit and total return separately
Decimal odds include the returned stake in the quoted total return per unit stake. Fractional odds quote profit relative to stake. Decimal 2.50 and fractional 3/2 therefore describe the same gross-return multiplier: a hypothetical one-unit stake returns 2.50 units in total if successful, including 1.50 units of profit. This is quotation arithmetic, not a recommendation to wager.
Convert American quotes by their sign
Positive American odds +150 quote 150 profit per 100 stake and convert to decimal 1+150/100 = 2.50. Negative odds −200 quote 100 profit per 200 stake and convert to decimal 1+100/200 = 1.50. For raw implied probability, take the reciprocal of decimal odds. Thus 2.50 implies 40%, while 1.50 implies about 66.6667% before any market-margin treatment.
| Decimal | Fractional | American | Raw implied probability |
|---|---|---|---|
| 2.50 | 3/2 | +150 | 40% |
| 1.50 | 1/2 | −200 | 66.6667% |
Do not turn a quote into an established true chance
The reciprocal is a break-even probability under the simplified payoff convention. It is not proof of the event's actual probability. Quoted markets may include a margin, and transaction terms, commissions or settlement rules can change real net payoffs. These are not silently modeled by the conversion tool.
Choose the proper market declaration
The Implied Probability Calculator converts one quote per line and treats overround separately. Only declare a complete market when all mutually exclusive and exhaustive outcomes from the same market are included. Read overround and proportional normalization before interpreting the normalized values. If you already have hypothetical outcomes and their probabilities and want a weighted net mean, use the Expected Value Calculator; quoted odds alone do not supply independently verified probabilities for that table.
Check the model behind your result
Use the Implied Probability Calculator for the supported calculation and review its stated assumptions before interpreting the output. Find related tools in the Statistics category, or browse the GreenCalc homepage for other calculation topics.
By GreenCalc Editorial Team · Updated 2026-10-26