Overround & Vig Calculator

What Is Overround?

Overround (also known as vig, juice, or the bookmaker's margin) is the percentage by which the sum of implied probabilities exceeds 100%. It's how bookmakers guarantee a profit regardless of the outcome. Understanding overround is essential for finding value and choosing the best bookmaker.

How to Calculate Overround

Step 1: Convert each outcome's odds to implied probability: (1 ÷ Decimal Odds) × 100

Step 2: Sum all implied probabilities

Step 3: Subtract 100 — the remainder is the overround

Example: A football match with odds 1.85 (Home) and 1.85 (Away) → 54.05% + 54.05% = 108.1%. Overround = 8.1%

What Are Fair Odds?

Fair odds remove the bookmaker's margin. They're what the odds would be if the market had 0% overround. The calculator above shows both — so you can see exactly how much the bookie is shaving off each outcome.

Formula: Fair Odds = 1 ÷ (Implied Probability ÷ Total Implied Probability)

What's a Good Overround?

• Under 2%: Excellent — typically found on betting exchanges (after commission)
• 2-5%: Competitive — sharp bookmakers on major markets
• 5-8%: Typical — most recreational bookies on popular markets
• 8-12%: Poor — often seen on minor markets or less competitive bookies
• Above 12%: Avoid — the margin is too high to find value

Overround vs Vig — Same Thing?

Technically, overround and vig (vigorish) refer to the same concept — the bookmaker's margin. In common usage, overround refers to the total percentage above 100% when summing all implied probabilities, while vig is sometimes expressed as the margin per unit staked. Our calculator shows both.

How to Beat the Overround

• Compare bookmakers — use our Implied Probability Calculator to find the lowest-margin odds
• Use betting exchanges — Betfair and similar platforms often have under 2% overround
• Focus on major markets — match odds on Premier League games have tighter margins than obscure leagues
• Dutch across bookies — our Dutching Calculator helps you back multiple outcomes at the best available odds

Frequently Asked Questions

What is overround in betting?

Overround is the built-in advantage a bookmaker has by pricing odds so that the sum of implied probabilities exceeds 100%. The excess is the bookie's guaranteed edge.

How do you calculate overround?

Convert all odds to implied probabilities, sum them, and subtract 100. Example: odds of 1.85 and 1.85 → 54.05% + 54.05% = 108.1% → overround = 8.1%.

What is a good overround?

2-5% is competitive for major markets. Under 2% is excellent. Above 8% is poor — look for better odds elsewhere.

What are fair odds?

Fair odds remove the bookmaker's margin. They're calculated by normalising implied probabilities to sum to exactly 100%. Fair odds are always higher (better) than the actual odds offered.

What is the difference between overround and vig?

They refer to the same concept — the bookmaker's margin. Overround is the percentage above 100% when summing all implied probabilities. Vig is sometimes expressed per unit staked. In practice, they're used interchangeably.