Vig, short for vigorish and also called juice, is the commission a bookmaker builds into its odds. It is how bookmakers make money: every price you see is slightly worse than a mathematically fair price, and the difference across all outcomes in a market is the bookmaker's margin. A vig calculator measures that margin from the odds themselves, and it can also show the fair, no-vig prices underneath.

The formula is straightforward. Convert each price to an implied probability by dividing 1 by the decimal odds, add those probabilities together, and subtract 100 percent. The excess is the overround, which is the vig. For a two-way market, vig percent equals the sum of 1 divided by each price, minus 1, multiplied by 100. That single number tells you how expensive the market is.

Here is the standard worked example. A two-way market priced at -110 on each side in American odds converts to decimal odds of about 1.91 on each side. Each side implies 1 divided by 1.91, which is about 52.38 percent. Added together they make 104.76 percent, so the vig is 104.76 minus 100, which is about 4.76 percent. In plain terms, for every 100 units of true probability, the bookmaker is pricing the market at about 104.76 units.

A vig calculator also shows fair, no-vig odds. To find them, divide each side's implied probability by the total. Here, 52.38 divided by 104.76 is 50 percent for each side, which converts back to decimal odds of 2.00. Those are the prices the market would offer if it took no commission. Comparing posted odds with fair odds shows exactly how much the margin costs you on each side, and it lets you compare the same market across bookmakers on equal terms.

A second example shows why vig differs by market. Take a two-way market at decimal odds of 1.80 and 2.10. Their implied probabilities are about 55.56 percent and 47.62 percent, totalling 103.17 percent, so the vig is about 3.17 percent. Removing the vig proportionally gives fair probabilities of about 53.85 percent and 46.15 percent, which convert to fair odds of about 1.86 and 2.17. Lower vig means better prices for bettors, which is why reduced-juice lines, such as -105 instead of -110, matter more than they first appear.

As a rough guide, vig under 3 percent is excellent and typical of sharp bookmakers and exchanges, 3 to 5 percent is competitive, 5 to 8 percent is average, and above 8 percent is expensive, which is common in niche markets and multi-leg parlays, where each leg carries its own margin. Three-way football markets usually carry more vig than two-way markets, simply because there are three prices to pad instead of two.

To use a vig calculator well, enter one complete market, use decimal odds or let the tool convert for you, and check that you have included every outcome. Missing an outcome makes the result incomplete, because the missing probability is part of the total. And remember what the calculator cannot do: fair odds are a mathematical adjustment, not a prediction of true probabilities, and removing the margin does not make a bet good value on its own.

Q: What is the difference between vig, overround and hold? A: Overround is how far combined implied probabilities sit above 100 percent. Vig, or juice, is the charge that creates it. Hold is the share of turnover a bookmaker expects to keep, which is related but not identical.

Q: What is a normal vig? A: Roughly 4 to 5 percent on a two-way line, nearer 2 percent at sharper books, and more on three-way football markets.

Q: Do fair odds predict the true probability? A: No. Fair odds remove the margin proportionally, but the result is still the market's estimate, not a proven true probability.