Margin (the "overround" or "vig") is the bookmaker's built-in cut. It is invisible on the betslip, permanent, and it is the reason most punters lose over time. Here is how to measure it on any market in under a minute.
Convert every price in the market to implied probability (1 ÷ odds), add them up, and subtract 1:
margin = (1/odds₁ + 1/odds₂ + 1/odds₃) − 1
A three-way football market at 2.10 / 3.40 / 3.60 gives 0.476 + 0.294 + 0.278 = 1.049 — a margin of 4.9%.
Margin is charged on every bet, win or lose. On a ₦1,000 stake in a market with a 7% margin, roughly ₦70 of expected value disappears the moment you click place. That is why the same bettor can be sharp on selection and still lose money over a season.
| Market margin | Cost on ₦100,000 staked | Reads as |
|---|---|---|
| 4% | ₦4,000 | competitive — major leagues, top books |
| 7% | ₦7,000 | typical |
| 10% | ₦10,000 | expensive |
| 15%+ | ₦15,000+ | avoid — usually niche markets, virtuals, specials |
Check the margin on the market you care about with the margin calculator, then compare the same market across two books. The difference between a 5% and a 9% margin on the same fixture is a permanent edge on every bet you place there — larger, over time, than any tip.
There is no "fair" — margin is the book's revenue. On major football markets, 4% to 6% is competitive in Nigeria; above 12% is expensive and you should shop elsewhere for that market.
Only in theory. If the implied probabilities of all outcomes sum to exactly 100%, the book takes no edge — the price is "fair". Exchange-style markets get close; retail books never do.