How do you read betting odds?

American odds use a plus or minus and a number. A minus figure such as minus 150 means you must stake 150 to win 100, marking the favorite. A plus figure such as plus 130 means a 100 stake wins 130, marking the underdog. Your original stake is returned on a win in both cases. Decimal odds, standard in Europe, express the total return per unit staked, so 2.50 returns 250 on a 100 stake including the stake. Fractional odds, traditional in Britain and horse racing, express profit relative to stake, so 3/1 wins 300 on a 100 stake.

Converting to implied probability is what makes odds legible. For a minus figure, divide the number by itself plus 100, so minus 150 implies 150 divided by 250, or 60 percent. For a plus figure, divide 100 by the number plus 100, so plus 130 implies 100 divided by 230, or about 43.5 percent. Doing this for both sides of a two-way market reveals the important structural fact: the implied probabilities sum to more than 100 percent, commonly 104 to 110. That excess is the vigorish or hold, and it is the operator's built-in margin, functioning the same way the zero does on a roulette wheel.

Two consequences worth internalizing. Because of the margin, breaking even requires winning meaningfully more than half your bets at standard pricing, and a bettor picking at random loses steadily rather than breaking even over time. And the odds represent the operator's balancing of money wagered as much as a forecast, so they encode market sentiment rather than pure probability. Parlays, which multiply several outcomes together, compound the margin at each leg, which is why they are heavily promoted and why their expected value is substantially worse than single bets. If gambling stops being entertainment with a budget attached, the National Council on Problem Gambling operates a confidential helpline.