How to read probability in betting
Probability is the foundation of every bet. Here's how to convert between odds and probability, understand the bookmaker margin, and interpret what prediction models are actually telling you.
What probability means in betting
Probability is a number between 0% and 100% that represents how likely an event is to happen. In football betting, every outcome — home win, draw, away win — has a probability. A 60% chance means the event is expected to happen 60 times out of 100.
Bookmakers express probability indirectly through odds. When you see odds of 2.00 on a team, the bookmaker is (roughly) saying that team has a 50% chance of winning. Learning to convert between odds and probability is the most fundamental skill in informed betting.
Decimal odds to probability
Most European bookmakers and prediction platforms use decimal odds. The conversion is simple:
Examples
The lower the odds, the higher the implied probability. Odds of 1.20 imply an 83% chance — the bookmaker thinks this outcome is very likely. Odds of 6.00 imply only a 17% chance.
Why probabilities don't add up to 100%
Here is something you will notice immediately: if you convert all three outcomes of a football match to implied probabilities, they add up to more than 100%.
Example
Arsenal vs Chelsea:
- Arsenal win: odds 1.85 → 54.1%
- Draw: odds 3.60 → 27.8%
- Chelsea win: odds 4.50 → 22.2%
- Total: 104.1%
The extra 4.1% is the bookmaker's margin (also called the overround or vig). It is how bookmakers guarantee profit regardless of the result. Every market has this built in.
To get the “true” implied probability, you can normalize by dividing each probability by the total:
- Arsenal: 54.1% ÷ 104.1% = 52.0%
- Draw: 27.8% ÷ 104.1% = 26.7%
- Chelsea: 22.2% ÷ 104.1% = 21.3%
These normalized probabilities add up to 100% and remove the bookmaker's margin.
Model probability vs bookmaker probability
When you use a prediction platform like oddsly, you see two different probability estimates for the same outcome:
- Model probability — What our AI calculates based on 70+ match features (form, ELO, xG, head-to-head, etc.)
- Bookmaker implied probability — What the odds tell you the bookmaker (and the betting market) believes
When these two numbers disagree significantly — for example, our model says 55% but the bookmaker implies 45% — that is a potential value bet. The model believes the outcome is more likely than the market is pricing in.
Confidence scores vs probability
You may also see a confidence score alongside probability. These are different concepts:
- Probability answers: “What is the chance this outcome happens?” — e.g., 55% chance of a home win.
- Confidence answers: “How sure is the model about its own estimate?” — e.g., High confidence means the data strongly supports the prediction; Low confidence means the model is uncertain.
A match can have a clear favourite (high probability) but low confidence if the data is sparse or contradictory. Conversely, a tight match (50/50 probability) can have high confidence if the model is very sure it is indeed a coin flip.
Key takeaway: Probability is the language of betting. Once you can convert between odds and probability, you can assess whether a bookmaker's price is fair, compare your own estimates against the market, and identify situations where the odds might be in your favour. This single skill separates informed bettors from recreational ones.