Every bet you place includes an invisible commission. If you don't know how to calculate it, you're paying a tax you don't even know about.
What odds represent
Odds aren't probabilities. They're distorted probabilities with a built-in margin that the bookmaker charges on every bet you place.
An odds price is the inverse of the implied probability the bookmaker assigns to an event, plus their margin. Odds of 2.00 imply a 50% probability. Odds of 4.00, a 25%.
From odds to implied probability
2.00
Odds = 50%
1.50
Odds = 66.7%
4.00
Odds = 25%
>100%
Total sum (margin)
The formula is: implied probability = 1 / odds. But these probabilities don't add up to 100%. They add up to more. That difference is the bookmaker's margin, also called overround or vigorish.
Summary: Odds = implied probability + margin. They always add up to more than 100%. That excess is what the bookmaker earns regardless of the outcome.
The margin: the invisible cost of every bet
Concrete example: A match with odds of 1.90 / 1.90. Implied probability of each side: 52.6%. Combined: 105.2%. That extra 5.2% is the margin. For every €100 staked, the bookmaker keeps €5.20 regardless of the outcome.
Major leagues
Margin 3-5%. More competition between bookmakers = better odds for you.
VS
Lower leagues / exotics
Margin 8-12%. Less coverage = the bookmaker charges more.
This connects directly with value betting: to beat the margin, you need to find odds that compensate for that extra cost.
Summary: The margin is the invisible commission you pay on every bet. It ranges from 3% to 12% depending on the league and bookmaker. Choosing where you bet is as important as choosing what you bet.
Track your bets, analyse your real yield and manage your bankroll with data, not intuition.
Compare across bookmakers — The one with the lowest % charges you least. Over 500 bets, that difference compounds.
Example: odds 1.85 and 2.05
54.05%
1/1.85
48.78%
1/2.05
102.83%
Total sum
2.83%
Bookmaker margin
Summary: Calculating the margin is simple: add the implied probabilities and subtract 100. The result is what the bookmaker charges you. Always compare across bookmakers.
Why margin matters more than you think
The maths don't lie: If your target yield is 3-5%, and the bookmaker margin is 5%, you need to be 8-10% better than the market just to break even. That's very hard.
Reducing the margin you pay (by choosing bookmakers with better odds) is equivalent to improving your picks. It's the easiest way to boost profitability without changing anything in your analysis.
It also explains why parlays are so damaging: the margin multiplies with each selection.
Summary: Reducing the margin you pay improves your profitability as much as improving your picks. And it's much easier: you just have to compare odds.
How to use this knowledge
Compare odds — The difference between 1.85 and 1.95 seems small, but over 500 bets it produces a notable improvement in yield.
Avoid markets with margin >8% — You're paying too much to play. Look for markets where competition between bookmakers benefits you.
Record by bookmaker — Compare your yield at each bookmaker. This way you can see if you're leaving money on the table.
With a good bet record you can see if you're leaving money on the table by not shopping for odds.
With StakeMaster: You can record the bookmaker for each bet and compare your yield by bookmaker. This way you spot where you get better odds and where you're paying more margin than necessary.
Summary: Compare odds before betting, avoid expensive markets and analyse your yield by bookmaker. Small margin savings turn into big profitability improvements.
Frequently asked questions
Do all bookmakers have the same margin?
No. Bookmakers like Pinnacle have margins of 2-3%, while others reach 6-8%. The difference directly affects your long-term profitability.
Does the margin change depending on sport or league?
Yes. Major European football leagues have low margins (3-5%). Lower leagues, player markets or exotic markets can have margins of 8-12% or more.
How can I find out which bookmaker offers the best margin?
Calculate the margin with the formula (1/odds1 + 1/odds2 - 1) x 100. Compare it across bookmakers for the same event. The one with the lowest percentage charges you the least.
If you want to track how much margin you're paying and how it affects your profitability, record your bets on StakeMaster and analyse your yield by bookmaker.
