Enter the odds in any format and instantly see the equivalent in the other three. Decimal is standard in Europe and Asia. Fractional is standard in the United Kingdom. American is standard in North America. Implied probability is what you actually need to assess value.
Enter the odds in one format. The other three update automatically.
Sports betting odds are quoted in four different formats depending on which market and region you are in. Each format expresses the same underlying information (the bookmaker's price on an outcome) but in a different way. Understanding the conversions is essential for comparing prices across bookmakers and for any quantitative analysis of value.
Decimal odds are the global standard for online sports betting. They express the total return per unit staked, including the original stake. Odds of 2.50 mean a 10 euro stake returns 25 euro (15 profit plus the 10 stake). Decimal odds are the easiest to compute with because the math is direct: payout equals stake multiplied by decimal odds.
Fractional odds show profit relative to stake. Odds of 3/1 mean you profit 3 units for every 1 staked. A 10 euro bet at 3/1 returns 40 euro (30 profit plus 10 stake). Fractional odds are still common in UK retail sportsbooks and on horse racing in particular, but most online operators have shifted to decimal as the default.
American odds use positive numbers for underdogs and negative numbers for favourites. A positive American odds line of +150 means you profit 150 dollars for every 100 staked. A negative line of -150 means you need to stake 150 dollars to profit 100. The zero point is at +100 or -100, which is equivalent to even money or 2.00 decimal.
Implied probability is what the price says about the likelihood of the outcome. It equals 1 divided by the decimal odds, expressed as a percentage. The sum of implied probabilities across all outcomes in a market is always above 100 percent (because the bookmaker builds in their margin). The amount above 100 percent is the bookmaker margin or vig.
Decimal to fractional: Decimal minus 1, expressed as a fraction. 2.50 becomes 1.50 to 1, or 3/2.
Decimal to American: If decimal is 2.00 or higher, American = (decimal - 1) x 100. If decimal is below 2.00, American = -100 / (decimal - 1).
Decimal to implied probability: 1 divided by decimal, times 100 percent.
Fractional to decimal: Numerator divided by denominator, plus 1. 5/2 becomes 2.50 plus 1, equal to 3.50.
American to decimal: Positive: (American / 100) + 1. Negative: (100 / abs(American)) + 1.
Implied probability to decimal: 100 divided by probability percentage. 40 percent equals 100 / 40 = 2.50.
These conversions are linear and there is no precision loss between formats. Decimal 2.10 is exactly 11/10 fractional, exactly +110 American, and exactly 47.62 percent implied probability. The only complication is that fractional odds are conventionally rounded to convenient values (5/2 instead of 49/20), which can introduce a small mismatch when converting back.
If you ever do quantitative betting analysis, you will work in implied probability rather than any of the three quoted formats. The reason is that probability is the only quantity you can add, multiply, and compare across markets. Decimal, fractional and American odds are different representations of the same probability, but they are not directly comparable across bookmakers because each builds in a different margin.
When evaluating whether a price has value, the question is always: do you think the real probability of the outcome is higher than the implied probability? If you think a team has a 50 percent chance to win and the bookmaker is pricing them at 2.10 (implied probability 47.6 percent), the bet has value. If you think the team has a 45 percent chance and the price is 2.10, the bet does not.
Sharp bettors do not think in terms of odds at all. They think in terms of probabilities and edges. The odds are just the input format. Once you convert to implied probability, every market becomes comparable.
Bookmakers do not offer fair odds. They build in a margin called the vig (short for vigorish) or the juice. The vig is the amount by which the sum of implied probabilities across all outcomes exceeds 100 percent. A two-sided market with both outcomes priced at 1.91 has implied probabilities of 52.36 percent each, summing to 104.72 percent. The 4.72 percent above 100 is the bookmaker margin.
Different bookmakers carry different margins. Pinnacle and SBOBet are sharp bookmakers that carry margins as low as 2 percent. Mainstream retail bookmakers like Bet365 typically carry 5 to 7 percent. Recreational-focused bookmakers can carry 10 percent or more. The lower the vig, the better the price for the bettor.
To compare like-for-like across bookmakers, convert each operator's price on the same outcome to implied probability, then strip out their proportional share of the vig. This gives the "fair" implied probability that operator is assigning to the outcome. The bookmaker with the highest fair implied probability on the side you want to bet is offering you the best price.
If you use the Kelly criterion or any other formal staking method, the formula expects decimal odds as input. Plugging in American or fractional odds will give wrong stake sizes. Always convert to decimal before staking calculations.
For mental math at the bookmaker counter, fractional odds have an advantage: at 3/1, you instantly know your potential profit per unit. For machine-based comparison across operators, decimal odds win because the math is trivial. For comparing American-style moneylines to alternative point spread bets, you usually need to convert American to decimal to compute the implicit edge.
One practical tip: if you regularly bet across multiple regions, set your default odds display on every bookmaker account to decimal. This avoids conversion errors during fast-moving live betting, and makes it much easier to spot value across operators.
The most common error in odds conversion is treating American positive and negative odds asymmetrically. The formula for converting positive to decimal is (American / 100) + 1. The formula for negative is (100 / abs(American)) + 1. They are not symmetric, and using one formula for both gives wrong results.
The second most common error is rounding too aggressively when converting decimal to fractional. 2.10 decimal is technically 11/10 fractional, but UK bookmakers will typically quote 11/10 only as a rounding of 2.20. Conversion tools should round to the nearest standard fractional notation, but always double-check the math when the fractional looks slightly off.
The third common error is forgetting that implied probability needs to be greater than the price's implied probability to have value, not greater than 50 percent. A 1.50 bet with 70 percent real probability has value (implied prob is 66.7 percent). A 3.00 bet with 30 percent real probability has value (implied prob is 33.3 percent). The threshold is always the price's implied probability, not any fixed number.
Daily football tips with 15%+ edge over bookmaker odds. Free, no signup, updated every morning.
Today's picks →