One price, four notations. Convert American, decimal and fractional odds and see the implied probability.
American → decimal: positive odds A give d = 1 + A/100; negative odds give d = 1 + 100/|A|.
Decimal → American: d ≥ 2.00 gives +100 × (d − 1); d < 2.00 gives −100 ÷ (d − 1).
Fractional n/m → decimal: d = 1 + n/m.
Implied probability: 1/d (this still contains the book's vig — see the no-vig calculator for fair probability).
+150 = decimal 2.50 = fractional 3/2 = 40% implied — a $100 bet returns $250 total ($150 profit).
−110 = decimal 1.909 = fractional 10/11 = 52.38% implied — a $100 bet returns $190.91 total ($90.91 profit).
Deep dive: How to read American odds →
Whatever your book displays — they are the same price. Decimal is easiest for math (payout = stake × decimal), which is why most calculators convert to decimal internally.
The win rate at which the bet breaks even: 1 ÷ decimal odds. It includes the bookmaker's margin, so the sum across all outcomes exceeds 100%.
American convention uses +100 ("even money") for a decimal 2.00. Below even money the sign flips to negative: 1.91 is −110, 1.50 is −200.
Expected value of a bet from your fair win probability and the offered price.
Strip the bookmaker margin from two- or three-way odds to reveal the fair price.
Check two or three prices for a guaranteed profit and split your stake exactly.