Odds to Probability Converter

In short A 40% chance is decimal odds of 2.50, fractional odds of 3/2, and American odds of +150. All four say the same thing, and each is a lossless rearrangement of the others — so the only reason there are four is history. Decimal odds are the total returned per unit staked, INCLUDING your stake, which makes them 1 divided by the probability and the easiest format to reason with. Fractional odds are the PROFIT per unit staked, excluding the stake, which is why 3/2 and 2.50 look different while meaning the same thing — that single distinction causes most of the confusion between the two. American odds are a positive number showing the profit on a 100 stake, or a negative one showing the stake needed to profit 100; they flip sign at even money, which is the 50% line. The number that matters is the implied probability, because it is the break-even point: a bet at these odds must win more than 40% of the time to profit. That is the only figure to compare with your own estimate. One caveat that is not arithmetic. A bookmaker's implied probabilities across all outcomes always sum to more than 100%, and that excess is the overround — their margin. So every implied probability from a real price is a little higher than what they actually believe, and the true break-even is a little lower.