How do bookmakers make money?

Bookmakers build a margin (overround) into every market by inflating the implied probability sum above 100%. The excess beyond 100% represents their theoretical profit regardless of which outcome wins. On a 2-way market with a 5% margin, each bettor effectively pays a 5% edge to the book.

What is overround in betting?

Overround is the sum of all implied probabilities (1 ÷ decimal odds) in a market. A fair 50/50 coin flip at true odds would total 100%. If the book offers 1.91/1.91, the total is 104.7% — the 4.7% excess is the overround representing built-in bookmaker profit.

Which bookmaker has the lowest margin?

Pinnacle consistently offers the lowest margin in sports betting, often under 2% on major football and tennis markets. Betfair Exchange is the fairest option post-commission for liquid markets. Mainstream bookmakers average 5–8% on main markets, rising to 10–15% on props and outright specials.

Understanding Bookmaker Margin (Overround) in 2026

What Is Margin?

Bookmaker margin (also called overround, juice, or vig) is the percentage by which the sum of all implied probabilities in a market exceeds 100%. A fair market would sum to exactly 100% — the excess above that is the bookmaker's built-in edge.

Overround Formula

Overround = Σ (1 ÷ decimal_odds) × 100

Sum of all implied probabilities across every outcome in the market

Worked Example: 3-Way Football Match

Bookmaker offers: Home 2.10 · Draw 3.40 · Away 3.60

Home implied: 1 ÷ 2.10 = 47.62%
Draw implied: 1 ÷ 3.40 = 29.41%
Away implied: 1 ÷ 3.60 = 27.78%
Total: 47.62 + 29.41 + 27.78 = 104.81%
Margin = 104.81 − 100 = 4.81%

For every £100 bet on this market, the bookmaker expects to keep £4.81 regardless of the result — on average, across a large sample.

Margin by Market Type

Market	Typical margin (soft book)	Typical margin (Pinnacle)
Premier League 1X2	5–7%	2–3%
Asian handicap	3–5%	1–2%
Over/Under 2.5	4–6%	2–3%
Player props	8–15%	N/A
Outright winner	10–20%	5–8%
Live in-play	8–15%	3–5%

Removing the Margin to Find Fair Odds

To find the fair (no-margin) probability of each outcome, divide each implied probability by the total overround:

Using the example above (Home = 47.62%, total = 104.81%):
Fair probability = 47.62 ÷ 104.81 = 45.43% → Fair odds = 1 ÷ 0.4543 = 2.201

The bookmaker offered 2.10 — you now know you are paying 4.81% margin on this market.

How to Use This in Practice

Calculate margin before betting to compare books on the same match
Prefer Asian handicap and over/under markets on high-liquidity matches — margins are tightest
Use Pinnacle or Betfair Exchange as your benchmark for fair pricing
Combine with line shopping to always find the lowest available margin