How to calculate the bookmaker's margin on a market
Convert every price in the market to an implied probability (1 divided by the decimal odds), add them up and subtract 100%. Prices of 1.90 and 1.90 give 52.63% + 52.63% = 105.26%, so the margin is 5.26% and the prices pay back 95% of stakes on average.
What the margin is
A bookmaker does not sell bets at cost. Each price is set slightly below the price that would be fair for the chance involved, and the difference is the margin. It is the bookmaker's charge for taking the bet, in the way a bureau de change builds its charge into the exchange rate.
You never see the margin printed as a fee. It only shows up when you add the prices of a whole market together. The margin calculator does that addition for you; the steps below show what it is doing.
The formula
D1 to Dn are the decimal odds of every possible outcome of one market. S is the total implied probability. Other names for the margin are overround, vig and juice; other names for payback are payout rate and return to player.
Step by step
- List every outcome of one market. A match result has three (home, draw, away). A "total goals over or under" line has two. Miss one and the sum is meaningless.
- Write each price as decimal odds. If the prices are fractions or American figures, convert them first, as shown in the guide on converting odds into implied probability.
- Divide 1 by each price. Keep four decimal places.
- Add the results. This is S.
- Subtract 1. What is left is the margin. Multiply by 100 for a percentage.
Illustrative example: a two-way market
Prices are 1.72 and 2.15. The implied probabilities are 1 ÷ 1.72 = 0.5814 and 1 ÷ 2.15 = 0.4651. Together: S = 1.0465. The margin is 4.65% and the average payback is 1 ÷ 1.0465 = 95.56%.
Illustrative example: a three-way market
Prices are 2.40, 3.20 and 3.10. The implied probabilities are 0.4167, 0.3125 and 0.3226. Together: S = 1.0517. The margin is 5.17% and the average payback is 95.08%.
The three-way case laid out as a table
| Outcome | Decimal odds | Implied probability (1 ÷ D) | Margin-free probability | Margin-free odds (D × S) |
|---|---|---|---|---|
| Home | 2.40 | 41.67% | 39.62% | 2.52 |
| Draw | 3.20 | 31.25% | 29.71% | 3.37 |
| Away | 3.10 | 32.26% | 30.67% | 3.26 |
| Total | 105.17% | 100.00% |
The figures are invented for the method and are not taken from any bookmaker.
Taking the margin back out
Once S is known, you can estimate what the prices would be without the margin. The simplest method shares the margin out in proportion: divide each implied probability by S.
In the table above, 41.67% ÷ 1.0517 = 39.62%, and 2.40 × 1.0517 = 2.52. The gap between 2.52 and the 2.40 on offer is the cost of that bet: every KES 100 of return at the margin-free price has become about KES 95.
This proportional method is an assumption. A bookmaker may load more of the margin onto some outcomes than others, and nothing in the prices tells you how it was shared. Treat margin-free numbers as a reasonable estimate, not a measurement of the true chances.
Margin and payback are not mirror images
People often say "5% margin, so 95% payback". That is close but not exact, and the gap grows with the margin. Payback is 1 ÷ S, not 1 minus the margin.
At S = 1.05 the payback is 95.24%. At S = 1.10 it is 90.91%, not 90%. At S = 1.20 it is 83.33%, not 80%. When someone quotes one figure, check which of the two it is.
What the margin means for your money
The average payback says how much of each shilling staked comes back over a very large number of bets, if stakes are spread across outcomes the way the prices are. At 95% payback, KES 1,000 staked in total returns KES 950 on average and costs KES 50.
The cost applies to turnover, not to your starting balance. If winnings are staked again, the same shillings pass through the margin again and again. A balance of KES 1,000 that is turned over five times has had KES 5,000 staked and has an average cost of about KES 250 at 95% payback. The reasoning is taken further in the guide on expected value.
In a single bet you will not notice the margin at all, because you either win or lose the lot. It is a long-run average, and that is exactly why it is easy to ignore and expensive to ignore.
Where the inputs come from
Regulation 23(1) of the Gambling Control (Conduct of Gambling Operations) Regulations, 2026 requires a licensee to clearly display betting odds, rules and terms applicable to each bet, and regulation 23(2) bars altering the terms of a bet after it has been accepted, except as permitted by law or approved rules. For casino games, regulation 20(2) requires a licensee to clearly display rules of games, odds, house edge and average return to the player.
So the prices you need for this sum must be visible before a bet is struck. The regulations do not set a maximum margin for bookmaking in the provisions cited here, and this site does not publish "typical" margins because it has no verified data on them.
What the margin does not tell you
It does not say which outcome will occur, and it does not make any bet a sound decision. A market with a low margin is cheaper on average than one with a high margin, nothing more. Margins also multiply when selections are combined, which is the subject of the guide on why accumulators carry more margin.
Questions and answers
Is the margin the same as the bookmaker's profit?
Not exactly. The margin is the average share built into the prices. What a bookmaker actually keeps on one event depends on how much was staked on each outcome and on which outcome happens.
Is a 5% margin the same as a 95% payback?
Nearly, but not exactly. Payback is 1 divided by the total implied probability. A margin of 5.26% gives a payback of 95.00%, and a margin of 5.00% gives a payback of 95.24%.
Can I calculate the margin from one price?
No. You need the prices of all outcomes of the same market, because the margin is the amount by which their implied probabilities together exceed 100%.
Do markets with more outcomes have higher margins?
The formula does not require it, since any number of outcomes can be priced to any total. This site has no verified data on how operators price different markets, so measure the market in front of you instead of assuming.
Does a lower margin mean I am more likely to win?
No. The margin affects how much a winning bet pays, not how often an outcome happens. A lower margin lowers the average cost of betting; it never turns that cost into a gain.
Sources
- Gambling Control (Conduct of Gambling Operations) Regulations, 2026, rr.20(2), 22, 23, accessed 2026-10-04
- Gambling Control Act, 2025 (No. 14 of 2025), s.2, accessed 2026-10-04