Three ways of writing the same thing
Decimal, fractional, and American are three formats for the same underlying information: how much you stand to win relative to your stake, plus the bookmaker's implied probability.
Decimal odds
Decimal odds show your total payout (stake + profit) per unit bet. Odds of 2.50 mean a €10 stake returns €25 (your €10 back plus €15 profit).
Fractional odds
Common in the UK. 3/1 means €3 profit for each €1 staked. Equivalent decimal: 4.00. 5/2 means €5 profit per €2 staked. Equivalent decimal: 3.50.
American odds
Positive numbers show profit per $100 stake. +150 = $150 profit on $100. Negative numbers show stake needed for $100 profit. -200 = $200 stake to win $100.
Implied probability
Implied probability = 1 / decimal odds. Odds of 2.00 imply 50% probability. Odds of 1.50 imply 66.7% probability. Odds of 4.00 imply 25% probability.
The bookmaker's edge
On a coin-flip event (two outcomes, each truly 50%), a fair book would offer decimal 2.00 on both sides. Real books offer 1.91 on both, each side implies 52.3% probability, summing to 104.7%. That 4.7% overage is the bookmaker's margin, also called vig or juice.
Why this matters
Beating the book means finding bets where your estimate of probability exceeds the implied probability by more than the margin. Over time, consistent edges of 2-5% on good stake management produce profit. Without that edge, the margin guarantees you lose.
Try our odds converter to switch formats quickly.
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