How to calculate and remove bookmaker margin

Bookmaker margin (also called vig, vigorish, juice, or overround) is the built-in fee that bookmakers add to their odds. It's the reason why the implied probabilities from a set of odds always add up to more than 100%.

In a fair coin flip, both outcomes have a 50% chance. Fair decimal odds would be 2.00 on each side. But a bookmaker might offer 1.91 on each side — implying 52.4% probability per side, totaling 104.7%. That extra 4.7% is the margin.

The margin is how bookmakers make money regardless of the outcome. It's effectively a tax on every bet you place.

Calculating margin is straightforward. Convert each outcome's odds to implied probability, sum them, and subtract 100%.

Formula:

Margin% = (1/Odds₁ + 1/Odds₂ + ... + 1/Oddsₙ - 1) × 100

2-way example: Home 1.90, Away 2.00

Margin = (1/1.90 + 1/2.00 - 1) × 100 = (0.5263 + 0.5000 - 1) × 100 = 2.63%

3-way example: Home 2.10, Draw 3.40, Away 3.60

Margin = (1/2.10 + 1/3.40 + 1/3.60 - 1) × 100 = (0.4762 + 0.2941 + 0.2778 - 1) × 100 = 4.81%

Try it yourself with the fair odds calculator.

Fair odds (or no-vig odds) are what the odds would be with zero margin — they represent the bookmaker's true probability estimate for each outcome.

The simplest method is proportional margin removal, which distributes the overround equally across all outcomes:

Fair Odds = Bookmaker Odds × (Sum of Implied Probabilities)

Or equivalently:

Fair Probability = Implied Probability / Sum of Implied Probabilities

Example: Home 1.90, Away 2.00 (margin 2.63%)

• Implied probabilities: 52.63% + 50.00% = 102.63%
• Fair Home probability: 52.63% / 102.63% = 51.28%
• Fair Away probability: 50.00% / 102.63% = 48.72%
• Fair Home odds: 1/0.5128 = 1.950
• Fair Away odds: 1/0.4872 = 2.053

These fair odds now sum to exactly 100% implied probability, giving you a clean baseline for value comparison.

Understanding margin has several practical applications:

• Evaluating bookmakers. Lower margin means better odds for you. A bookmaker with 2% margin gives you significantly more value per bet than one with 8% margin.
• Calculating expected value. To know if a bet has positive expected value, you need to compare your odds against the true probability — which requires removing the margin.
• Measuring CLV. Closing line value should be calculated using no-vig closing odds, not raw bookmaker odds. Using raw odds understates your CLV because of the margin.
• Comparing lines. When shopping for odds across bookmakers, understanding margin helps you evaluate which book is truly offering the best price, not just the highest raw number.

Margins vary significantly across bookmakers:

• Sharp bookmakers (Pinnacle, ISN): 1.5-3% on major markets. These are the fairest odds available.
• Betting exchanges (Betfair): 0% margin on odds, but charge 2-5% commission on winnings. Effective margin varies by market liquidity.
• Mid-range bookmakers: 3-6% on major sports, higher on niche markets.
• Retail/soft bookmakers: 5-10%+ on most markets. Significantly worse odds but often offer promotions and don't limit winners quickly.

The margin also varies by market type within the same bookmaker. Main markets (match winner, totals) typically have the lowest margin, while exotic or player prop markets have much higher margins.