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Implied Probability
Implied probability is the chance of an outcome that a price represents. Every odds format is just a way of quoting a payout, and the payout fixes the break-even win rate: decimal odds of 2.50 imply 1 divided by 2.50, or 40 per cent. If the outcome happens more often than that, the price is good for the bettor; less often, it is not. A price is information about the market, never a promise.
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Implied Probability Formula for Every Odds Format
Derive implied probability for American, decimal and fractional odds, then see why Bovada's -1000/+600 pair sums to 105.19% and what that overround means.
SonicBet Odds Bulletin ·
How do you convert odds into implied probability?
- Decimal odds: divide 1 by the odds. 1.80 implies 55.6 per cent.
- American odds, negative (favourite): divide the number by itself plus 100. -150 gives 150 / 250, or 60 per cent.
- American odds, positive (underdog): divide 100 by the number plus 100. +200 gives 100 / 300, or 33.3 per cent.
- Fractional odds a/b: divide b by a plus b. 5/2 gives 2 / 7, or 28.6 per cent.
Our implied probability formula bulletin derives each of these from the payout definition, so you can check any converter by hand.
Why do the probabilities add up to more than 100 per cent?
Because the bookmaker builds its margin into the prices. Convert both sides of a standard -110 / -110 line and each implies 52.38 per cent, which sums to 104.76 per cent. The extra 4.76 points is the overround. It means no single price on the board is the market's fair estimate: each one carries a share of the margin. To get a fair probability you remove the margin first, which is what the vig lane covers.
What does implied probability tell you about a bet?
It turns a price into a question you can actually answer: does this outcome happen more often than the price needs? A bettor who thinks a team wins 45 per cent of the time should only take odds that imply less than that, after accounting for the margin. Implied probability does not tell you who will win. It tells you what the market is charging for the belief that they will.
How do prices move as probabilities change?
The conversion is not linear. A move from -110 to -130 shifts the implied chance by about four points; the same 20-point move from +300 to +320 shifts it by about one. That is why line movement is best read in probability terms, not in raw odds, as the line movement bulletins do.
How SonicBet covers implied probability
Every bulletin works the conversion through with real prices before drawing any conclusion. Start with the formula bulletin, then remove the margin with the vig lane.