Bookmaker margin explained

The bookmaker's margin is the price of every bet you place. It is not listed anywhere on the slip, but it is in the odds, and two minutes of arithmetic pulls it out. Once you can measure it, you can compare books on the same market, see which bet types cost the most, and understand why a sportsbook can lose on a game and still have a good month. Every calculation here is shown step by step.

Overround and margin

Each price implies a probability: 1 divided by the decimal odds. In a fair market those probabilities would add up to exactly 100%. Sportsbooks shade every price down a little, so the total comes out above 100%. That total is the overround.

• Overround = 1/D1 + 1/D2 + ... (all outcomes)
• Payout = 1 / overround (what bettors get back over time if money is balanced)
• Margin = 1 - payout

You will also see "vig" or "juice" quoted as 4.76% for the same line: that is the overround minus 100%. Both describe the same price; 1 - 1/overround is the share of stakes kept, which is why we use it. If you need American odds converted first, use the odds converter or our guide to reading odds.

Margins on different market shapes

The soccer row uses the odds from Hegarty and Whelan's example in their VoxEU column; the others are illustrative prices. Check on the futures row: 1/3 + 1/3.5 + 1/4 + 1/4.5 = 1.0913; 1 / 1.0913 = 0.9164; margin 8.36%.

The pattern: more outcomes, more room for margin. Futures with dozens of teams can carry far more than the four-runner example. Props and same-game parlays have no published margin figures, but each leg carries its own margin; see same game parlays.

Fair odds: taking the margin out

Divide each implied probability by the overround to get the book's no-margin view.

This proportional method is the simplest. It spreads the margin evenly across outcomes. Research on soccer markets, including Hegarty and Whelan's study of 84,230 European matches, found that longshots tend to carry more of the margin than favourites in 1X2 markets, so the proportional method slightly understates the fair price of favourites in those markets.

Two-way prices at a glance

Most main markets are two-way lines with the same price on both sides. The margin for each common price:

Every five cents on the line adds about two points of margin. A book quoting -115 / -115 on totals charges almost three times the margin of one quoting -105 / -105.

Margin vs hold: what books really keep

Margin is what the prices imply. Hold is what a book actually keeps: winnings divided by the amount bet, reported by regulators after results are in.

Nevada's Gaming Control Board, statewide, twelve months from August 1, 2025 to July 31, 2026:

In Ontario, iGaming Ontario reported C$724 million of betting revenue on C$11.4 billion of betting wagers for fiscal 2024-25; dividing one by the other gives a hold of about 6.35%.

Hold runs above the -110 margin, and the regulator does not break down why. The likely reasons, in our reading: a lot of money goes into parlays and props, which carry higher margins; money does not split evenly between sides; and favourite-longshot pricing makes popular longshot bets more expensive.

What the margin costs you

The margin is charged on turnover. The more you bet, the more you pay, whatever your bankroll.

• 50 bets of C$20 at a 4.55% margin: C$1,000 turnover, about C$45.50 average cost.
• The same 50 bets as three-leg parlays: built-in edge about 13.03%, about C$130 average cost.

How to pay less of it

• Compare prices. The same NHL total at -110 at one book and -105 at another is a margin of 4.55% versus about 2.4%. Holding two or three accounts is the cheapest edge a bettor can get; see how to choose a sportsbook.
• Prefer main markets. Moneylines, spreads and totals are usually priced tighter than props and futures.
• Keep parlays short. The margin compounds per leg; see parlays explained.
• Use boosts and promos on purpose. A genuine odds boost can remove the margin on one bet.

None of this makes betting a source of income. It makes it cheaper entertainment. Set the budget first with our bankroll management guide, and see responsible gambling for help in your province. For the prices themselves, compare the books on the betting sites page.