How to read betting odds: American, decimal, and fractional

American odds are the default in the US and Canada. Negative numbers show how much you must risk to win $100; positive numbers show how much you win on a $100 bet.

A line of -150 means you wager $150 to profit $100. A line of +130 means a $100 bet returns $130 in profit. The break-even win percentages are 60% and 43.5% respectively — and the book takes its cut in the gap between those numbers on opposing sides of the same game.

To convert American odds to implied probability: for negative odds, divide the absolute value by (absolute value + 100). For +130, divide 100 by (130 + 100) = 43.5%.

Decimal odds are the global standard — common in Europe, Australia, and on most international exchanges. The number represents your total return per dollar staked, including your stake.

Odds of 1.91 on a $100 bet return $191 in total ($91 profit). Odds of 2.50 return $250 total ($150 profit). To find implied probability, just divide 1 by the decimal: 1 / 1.91 = 52.4%. Decimal odds below 2.00 are equivalent to negative American odds; above 2.00 they are positive.

Fractional odds are traditional in the UK and Ireland and still common for horse racing. They express profit relative to stake: 5/2 means you profit $5 for every $2 wagered ($2.50 profit per $1 staked).

To convert fractional to implied probability, divide the denominator by the sum of numerator and denominator: 2 / (5 + 2) = 28.6%. Even-money is 1/1 (50% implied). Fractional odds are less common on US sports but occasionally appear in futures markets.

Every format bakes in the sportsbook margin (the juice, or vig). A standard -110 / -110 line has roughly 4.5% hold — the book keeps about $4.50 of every $100 wagered long-run. That is why converting odds to no-vig probabilities matters: the posted line overstates the implied probability of each side by the same proportion.

Value betting is finding lines where your estimated true probability exceeds the no-vig implied probability. The format you use does not change the math, but learning to read all three fluently lets you compare prices across any book in the world.

Convert through decimal odds, which every format maps to directly. For positive American odds, divide by 100 and add 1: +150 becomes 2.50. For negative American odds, divide 100 by the absolute value and add 1: -110 becomes 1.91 and -150 becomes 1.67. Decimal odds always include the stake, which is why even money is 2.00.

Going back, a decimal of 2.00 or more becomes American by subtracting 1 and multiplying by 100: 2.50 becomes +150. Below 2.00, divide -100 by (decimal − 1): 1.91 becomes -100 / 0.91, about -110. For fractional odds, divide the numerator by the denominator and add 1: 5/2 becomes 3.50, or +250.

Check the result with implied probability. 5/2, 3.50 and +250 should all give the same answer, and they do: 1 / 3.50 = 28.6% and 100 / 350 = 28.6%. If two formats disagree by more than rounding, one conversion went wrong.

The break-even win rate is the implied probability of the price you bet. At -110 it is 110 / 210 = 52.38%. At -120 it is 54.55% and at -200 it is 66.67%. At +100 it is 50%, at +150 it is 40% and at +200 it is 33.33%.

You can check -110 by hand. Bet $110 a hundred times and win W of them. Each win pays $100 and each loss costs $110, so you break even when W × 100 = (100 − W) × 110. That gives W = 52.38.

A common misreading is that plus odds mean a better bet. They only mean a bigger payout for a less likely outcome. A +200 underdog that wins 30% of the time loses money, and a -200 favorite that wins 70% of the time makes money. Value comes from the gap between the price and the true chance, not from the sign.

Add up the implied probabilities of every side, then divide each side by that total. At -110 / -110 both sides imply 52.38%, for a total of 104.76%. Each fair probability is 50%, and the hold is 1 − 1 / 1.0476, about 4.5%.

Uneven lines work the same way. At -150 / +130 the implied probabilities are 60.00% and 43.48%, for a total of 103.48%. Divided by 1.0348, the favorite is 57.98% and the underdog is 42.02%. In American odds, that fair line is about -138 / +138. These no-vig numbers are what you compare your own estimate against.

This proportional method assumes the book spreads its margin evenly across both sides. Books often take more of it from the longshot, so treat the result as an estimate. It is still far closer to fair than the posted price. Where a low-margin book or exchange prices the same game, its line is a second check.