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A bookmaker's margin is the amount by which the implied probabilities of every outcome in a market add up to more than 100%. It is built into the odds, so across everyone betting on a market, less comes back than is staked.
Decimal odds convert to an implied probability by dividing 1 by the odds. Odds of 1.91 imply 1 / 1.91 = 52.36%. If both sides of an even market are priced at 1.91, the two probabilities add up to 52.36% + 52.36% = 104.71%. A fair price on each side would be 2.00, which implies 50% and a total of 100%. The extra 4.71% is the margin.
Take a football match priced at 2.45, 3.30 and 3.10. The implied probabilities add up to 40.82% + 30.30% + 32.26% = 103.38%, so the margin is 3.38%. Removing the margin in proportion gives the fair odds in the last column.
| Outcome | Odds | Implied probability | Odds with margin removed |
|---|---|---|---|
| Home | 2.45 | 1 / 2.45 = 40.82% | 2.53 |
| Draw | 3.30 | 1 / 3.30 = 30.30% | 3.41 |
| Away | 3.10 | 1 / 3.10 = 32.26% | 3.20 |
Fair odds = offered odds × 1.0338. To try your own market, use the margin calculator.
The expected payout on a market is 1 divided by the total. Here that is 1 / 1.0338 = 96.73%, so on average 96.73 comes back for every 100 staked and the cost is 3.27. The margin (3.38%) and the cost (3.27 per 100 staked) are close but not the same number, because one is measured against the probabilities and the other against your stake.
Combine selections and each one carries its own margin. Three selections each priced at 1.91, where the fair price is 2.00, give combined odds of 1.91 × 1.91 × 1.91 = 6.97 against a fair 2.00 × 2.00 × 2.00 = 8.00. The expected payout is 6.97 / 8.00 = 87.10%, a cost of 12.90 per 100 staked, against 4.50 for a single selection at the same price. The betting cost calculator does this for any number of selections and turns it into a weekly, monthly and yearly figure.
The margin is why a record of your own stakes and returns matters: it shows your real result, not the one you remember. How to see what betting really costs you explains what to record.
It is the amount by which the implied probabilities of all outcomes in a market add up past 100%. Prices of 1.91 on each side of a two outcome market imply 52.36% each, a total of 104.71%, so the margin is 4.71%.
No. A margin of 3.38% on a three outcome market means a total of 103.38%. The expected payout is 1 divided by 1.0338, which is 96.73%, so the cost is 3.27 for every 100 staked.
Each selection carries its own margin and the margins multiply. Three selections priced at 1.91 each, where fair odds would be 2.00, cost 12.90 per 100 staked on average, against 4.50 for one selection at the same price.
It means that, across everyone betting, more is staked than is returned, so the average bettor loses over time. It is not a prediction for one person: individual results vary a great deal, and some people lose much more than the average.
Zort is a bet tracker for iPhone and Android. You photograph or screenshot a slip for a bet you have already placed, check what Zort read, and save it. Zort then shows your profit and loss, ROI and win rate. It is not a betting app: it takes no bets, gives no tips and links to no bookmakers. It is free to download, and this page lists exactly what it does and does not do. For adults aged 18 and over.
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