Implied probability is the bridge between the odds you see and the chances they represent. Every price can be translated into a percentage, and doing so is one of the most useful habits a bettor can build because it lets you compare a bookmaker's view with your own.
The formulas are simple enough to do in your head with a little practice, and understanding them unlocks concepts like margin and value that separate thoughtful bettors from the crowd.
Converting Decimal Odds
To turn decimal odds into implied probability, divide 1 by the odds and multiply by 100. Odds of 2.00 give 1 ÷ 2.00 = 0.50, or 50%. Odds of 5.00 give 1 ÷ 5.00 = 0.20, or 20%. The higher the odds, the lower the implied chance.
Converting Fractional Odds
For fractional odds written as A/B, the implied probability is B ÷ (A + B), times 100. For 3/1, that is 1 ÷ (3 + 1) = 0.25, or 25%. For 5/2, it is 2 ÷ (5 + 2) ≈ 0.286, or about 28.6%. If fractions feel awkward, convert to decimals first using our odds format guide.
Why the Market Totals over 100%
Add the implied probabilities of every outcome in a market and you will get a figure above 100%. That excess is the bookmaker's margin. A two-horse market priced at 1.90 each implies 52.6% per side, totalling 105.2%, and that extra 5.2% is the book's built-in edge.
Removing the Margin
To estimate the "true" probability the market is pricing in, you can scale each implied probability so the market totals 100%. This gives a fairer sense of the odds behind the odds, though it is an estimate rather than a certainty.
Using Implied Probability in Practice
Once you can read a price as a percentage, you can ask the key question: do I think this outcome is more likely than the odds suggest? If your estimate beats the implied probability, you may have found value. Model the returns in the Bet Calculator Betmentor so the payoff sits alongside the probability in front of you.
A Quick Reference
- 2.00 = 50%
- 3.00 = 33.3%
- 4.00 = 25%
- 5.00 = 20%
- 10.00 = 10%
Commit a handful of these to memory and you will read any market faster, which feeds directly into spotting value.