Implied Probability — How to Read Betting Odds and Find Value
Odds Are Probabilities in Disguise
Every price is a disguised probability with margin added. When a book sets odds of 2.00, it's saying "we think the probability is about 50%". But not exactly 50% — the margin distorts the picture. Understanding this is the first step to professional betting and finding value bets.
The Conversion Formula — Simple and Important
Implied probability = 1 / decimal odds × 100%. The table: 1.20 = 83.3%, 1.50 = 66.7%, 1.80 = 55.6%, 2.00 = 50.0%, 2.50 = 40.0%, 3.00 = 33.3%, 4.00 = 25.0%, 5.00 = 20.0%, 10.00 = 10.0%. It's worth memorising — it lets you size up any price instantly.
The inverse is useful too: odds = 1 / (probability / 100). If a Poisson model gives 62% on Under 2.5, the "fair" price = 1 / 0.62 = 1.61. If the book offers 1.85, that's above fair, so the edge is positive.
The Bookmaker Margin — a Hidden Tax
Add up the implied probabilities of all outcomes of a match. The result won't be 100% but 105-110%. The difference is margin. Example: Real Madrid 1.30 (76.9%), draw 5.50 (18.2%), Getafe 10.00 (10.0%). Sum: 105.1%. Margin: 5.1%.
Margin means ALL prices are shortened. Without it, Real would be 1.37 not 1.30, the draw 5.78 not 5.50, Getafe 10.51 not 10.00. Margin is uneven — the favourite is usually loaded more, which creates a systematic advantage for backing less popular outcomes.
The "Fair" Price — Removing Margin
Fair probability = implied probability / sum of all probabilities. In our example: fair P(Real) = 76.9% / 105.1% = 73.2%. Fair odds = 1/0.732 = 1.37. The book offers 1.30 — margin on Real = 5.1%. For Getafe: fair P = 10.0% / 105.1% = 9.5%, fair odds = 10.51. The book offers 10.00 — margin = 4.9%. The margin is almost identical, but in absolute terms it "weighs" more on the favourite.
Finding Value Through Implied Probability
The algorithm: compute the implied probability, compute the true probability via the model, compare. If true is higher — a value bet. Compute edge = (true × odds) - 1. Size the stake via the Kelly Criterion.
Example: Under 2.5, odds 1.85. Implied: 54.1%. Our model: 63%. Edge = (0.63 × 1.85) - 1 = +16.6%. A strong value bet — published in the Telegram channel.
Why Odds Are Not Pure Probability
Odds are a market price, not a probability. They depend on bet volume, an event's popularity and the book's position. Manchester City attract millions of bets — the price is polished. Under 2.5 in an RPL match draws a hundredth of that, and errors are likelier. That's where a mathematical model finds the most edge. All results are open — verify them.