Bookmaker odds are not predictions of the score — they are probabilities in disguise, adjusted to guarantee the bookmaker a profit. Learn to convert odds into the probability they imply, then strip out the built-in margin, and you can see what the market actually thinks — the single most useful skill in football betting.
Odds are implied probability
Every decimal odd converts directly to a probability:
Implied probability = 1 ÷ decimal odds
| Decimal odds | Implied probability |
|---|---|
| 1.50 | 66.7% |
| 2.00 | 50.0% |
| 3.40 | 29.4% |
| 5.00 | 20.0% |
So odds of 2.00 mean the market thinks the outcome happens half the time. If your estimate is higher than the implied probability, you may have found a value bet.
The overround (the bookmaker's margin)
Add up the implied probabilities for all outcomes of a match and they sum to more than 100%. That excess is the overround — the bookmaker's built-in margin.
| Outcome | Odds | Implied prob |
|---|---|---|
| Home | 2.10 | 47.6% |
| Draw | 3.40 | 29.4% |
| Away | 3.80 | 26.3% |
| Total | 103.3% |
That 3.3% over 100% is the margin. It is why betting every outcome guarantees a small loss, and why beating the bookmaker long-term is hard.
Removing the margin to find the true price
To recover the market's genuine probability estimate, divide each implied probability by the total:
- True home prob = 47.6% ÷ 103.3% = 46.1%
- True draw prob = 29.4% ÷ 103.3% = 28.5%
- True away prob = 26.3% ÷ 103.3% = 25.4%
Now the three sum to 100%. These vig-removed probabilities are the market's honest opinion — and the benchmark we compare our model against in how our predictions work. When our Poisson model disagrees with the de-margined market by a wide margin, that is a signal worth investigating.
Why the market is hard to beat
Bookmaker odds aggregate the opinions of thousands of sharp bettors and adjust as money flows in. For top leagues, the de-margined price is an extremely good probability estimate. Our edge is not "beating the market everywhere" — it is finding the specific markets and fixtures where the price has room to be wrong, then publishing the result openly on our track record.
Frequently asked questions
How do you convert betting odds to a percentage?
For decimal odds, divide 1 by the odds: 1 ÷ 2.50 = 0.40, or 40%. That is the implied probability before the bookmaker's margin is removed.
What is the overround in betting?
The overround (or "vig") is the amount by which a market's implied probabilities exceed 100%. It represents the bookmaker's built-in margin. A typical football 1X2 market runs a 5–8% overround.
What does removing the vig mean?
Removing the vig (de-margining) rescales each outcome's implied probability so they sum to 100%, revealing the market's true probability estimate stripped of the bookmaker's margin. It is the fairest way to compare bookmaker prices to your own model.
Do lower-margin bookmakers offer better value?
Yes. A market with a smaller overround returns more of your stake over the long run. This is why Asian handicap markets, which often run margins of 1–3%, can offer better value than higher-margin markets covering the same match.
