Calculate the bookmaker margin (vig/overround) on any market and find the true fair-value odds with no bookmaker edge.
Enter the bookmaker odds for each outcome. Works for any market: 1X2, BTTS, Asian handicap, etc.
Enter decimal odds for at least 2 outcomes and click Calculate Margin.
Overround (also called the 'book') is the sum of implied probabilities for all outcomes in a market expressed as a percentage. A truly fair market would sum to exactly 100%, but bookmakers inflate the odds to create a margin — for example, an overround of 105% means the market adds up to 105% favourable to the bookie.
Vig, vigorish, or juice is the bookmaker's commission built into the odds. It is calculated as: vig = (overround − 100) / overround × 100. A 5% overround translates to roughly 4.76% vig — meaning the bookmaker expects to keep about £4.76 of every £100 wagered over the long run.
For football main markets, a margin below 4% is competitive. Betting exchanges typically have a margin of 0–2% (they charge separate commission). High-street bookmakers usually sit between 5–10%, and exotic or novelty markets can exceed 15%. Always shop for the lowest margin to maximise value.
Fair-value odds remove the overround so that all implied probabilities sum to 100%. For each outcome: fair_odds = decimal_odds × overround / 100. For example, if Home Win is priced at 2.00 in a 105% book, fair odds = 2.00 × 1.05 = 2.10.
Yes — a high overround significantly reduces your long-term expected return. On a 10% margin market you are starting every bet with a 10% disadvantage. Use the margin calculator to compare bookmakers before placing a bet, and favour those offering the lowest margin on the market you want.
Every bookmaker builds a profit margin into their odds — this is called the overround or vig (vigorish). It ensures the bookmaker makes money regardless of which outcome wins. Understanding how to measure this margin is an important skill for any serious bettor.
Convert each outcome's decimal odds to an implied probability (1 ÷ odds × 100), then sum all probabilities. A fair market sums to 100%. A market summing to 105% has a 5% overround in favour of the bookmaker — the extra 5% represents their edge.
A higher margin means you need to win more often just to break even. On a 10% margin market you need to win more than 52.4% of 50/50 bets to profit. By shopping for bookmakers with lower margins — or using exchanges — you reduce this built-in disadvantage and improve your long-term expected return.
Convert between decimal, fractional, and American odds and calculate potential payouts.
Combine up to 10 selections and instantly see your parlay payout, profit, and implied probability.