Implied probability is the percentage chance of winning that betting odds represent, and it is the first step in deciding whether a price is good or bad.

For decimal odds, divide 1 by the odds: 2.50 implies 40%. For negative American odds, divide the odds by the odds plus 100: -110 implies 52.4%.

For positive American odds, divide 100 by the odds plus 100: +150 implies 40%. These raw figures include the bookmaker's margin, so they add up to more than 100% across all outcomes.

Remove the margin by dividing each raw probability by the total, and compare the result with your own estimate: bet only when your estimate is higher than the implied probability by a clear margin.