Every bookmaker in the world charges you the same way: by pricing a market so the implied probabilities add up to more than 100%. The excess is the margin, and it is the closest thing betting has to a shelf price. Unlike a bonus, it applies to every bet you ever place.
What a margin actually is
A fair coin toss is 2.00 each side. Each price implies a 50% chance, and the two add to exactly 100%. No bookmaker offers that, because there would be nothing in it for them. Instead you see 1.91 and 1.91 — each implying 52.36%, adding to 104.72%. That 4.72% is the overround, also called the vig or the margin.
The number tells you what proportion of your turnover the bookmaker expects to keep. It does not predict whether any individual bet wins. It predicts, quite reliably, what happens to a thousand of them.
The one formula you need
Implied probability = 1 ÷ decimal odds. Add the implied probabilities of every outcome in a market, subtract 100, and you have the margin as a percentage.
Why it matters more than any bonus
A £30 welcome offer is claimed once. A 1.5-point difference in margin applies to every bet for as long as you hold the account. On £50 stakes, fifty bets a season, that gap is roughly £37 — more than the bonus, quietly, without any wagering requirement to read.
The bonus is the advertising. The margin is the price. Almost every bettor reads the first and ignores the second.
Ellis Hartnoll, Head of Testing
- Margins vary far more between bookmakers than most bettors expect — 3.4% to 5.6% across our current guide.
- They vary within a bookmaker too: main lines are sharp, player props are not.
- A sharper price improves every bet you place, including the ones you would have placed anyway.
Measuring a margin in two minutes
You need one market, the decimal prices, and a calculator. Do it on a market you actually bet, not a headline one — bookmakers price their shop windows tightly and their back rooms loosely.
Two-way markets
- Take the two prices. Home 1.91, Away 1.99 on a match handicap.
- Convert each to a percentage. 1 ÷ 1.91 = 52.36%. 1 ÷ 1.99 = 50.25%.
- Add them together. 52.36 + 50.25 = 102.61%.
- Subtract 100. The margin is 2.61% — a sharp market by any standard.
Do this on three bookmakers
Take the same market at three sites and compare the three totals. Ten minutes of arithmetic will tell you more about where to bet than any review, including ours.
Three-way markets
Football match result markets have three outcomes, so add three implied probabilities instead of two. A typical Premier Division 1X2 at a mainstream bookmaker runs 104% to 105%. Anything under 103% is genuinely sharp; anything over 107% is expensive enough to avoid.
What the numbers looked like across fifteen bookmakers
We price the same forty markets every month. The table below is the August 2026 average for the eight bookmakers currently in our guide, with the third column showing what the margin costs on a £50 bet in expectation.
| Bookmaker | Avg margin | Cost per £50 | Note |
|---|---|---|---|
| Kestrel | 3.4% | £1.70 | Lowest measured margin in our August guide |
| NovaBet | 3.9% | £1.95 | Sharpest of the market-leading brands |
| Marlin | 4.1% | £2.05 | Best all-round product, third on price |
| Bramble | 4.3% | £2.15 | Deep bet builder, mid-table pricing |
| Stadion | 4.6% | £2.30 | Live specialist; you pay for the product |
| Harbour | 4.9% | £2.45 | Fast payments, ordinary prices |
| NineLine | 5.1% | £2.55 | Beginner-friendly, expensive |
| Quaystone | 5.6% | £2.80 | Highest margin we measured |
The spread between top and bottom is 2.2 points. On £50 a bet that is £1.10 of expected cost per bet — the difference between a season that is roughly break-even and one that is not.
Three mistakes people make
- Measuring the shop window. Comparing only Premier Division match odds tells you which bookmaker wants to be compared, not which is cheapest on what you bet.
- Ignoring boosted prices. A boost applied to a wide market can still be worse than a rival’s standard price. Convert both before you decide.
- Assuming margin equals value. A sharp bookmaker is cheaper, not generous. It improves your expected return; it does not make a losing selection win.
A cheaper price is not a winning bet
Reducing the margin narrows the house edge. It does not remove it. Nothing on this page makes betting profitable, and no staking plan changes that arithmetic.
Where to go next
If this is new to you, read the odds guide first, then hold three accounts and take the best available price every time. Line shopping is the only edge available to every bettor without exception, and margin comparison is how you decide which three accounts to hold.
