Odds converter

Decimal, fractional and American odds are three notations for the same thing: how much a winning bet returns. Decimal odds count the whole return per unit staked, stake included. Fractional odds count only the winnings per unit staked. American odds count the winnings on 100 (positive odds) or the stake needed to win 100 (negative odds).

From fractional a/b to decimal:

decimal = a / b + 1

From American to decimal:

+A: decimal = A / 100 + 1   |   -A: decimal = 100 / A + 1

From decimal to American:

decimal ≥ 2: +(decimal - 1) × 100   |   decimal < 2: -100 / (decimal - 1)

Implied probability, from decimal:

probability = 1 / decimal

Implied probability is what the odds say the chance is. It is not the real chance: a book adds a margin, so the implied probabilities of every outcome in a market add up to more than 1. Take two outcomes priced at 1.91 each: 0.5236 + 0.5236 = 1.047. The 0.047 (4.7%) on top is the book's overround. Our no-vig calculator takes it out and shows the fair odds.

When the best prices for every outcome, taken from different books, have implied probabilities that add up to less than 1, the market has a surebet: stake each outcome in the right proportion and every result returns more than the total staked. The surebet calculator does that split.

Fractions are the nearest simple fraction, the way books round them (1.33 shows as 1/3, which is 1.333..., and 1.91 as 10/11).