Every sportsbook price includes a margin, so the probabilities implied by the odds add up to more than 100%. Learning to calculate no-vig odds lets you strip that margin out and estimate the fair probability the market is really suggesting. This guide shows the method with a full worked example you can reproduce with a calculator.
What “Vig” Means
Vig, short for vigorish (also called juice or the overround), is the bookmaker’s built-in fee. In a fair two-way market the implied probabilities would sum to exactly 100%. In practice they sum to something higher, and that excess is the margin. If you are new to converting prices, start with how to read betting odds.
Step 1: Convert Each Price to Implied Probability
For negative American odds, implied probability = |odds| ÷ (|odds| + 100). For positive odds, it is 100 ÷ (odds + 100). For decimal odds, it is 1 ÷ decimal.
Worked Example: A -115 / -105 Market
Imagine a two-way spread market where Side A is -115 and Side B is -105.
- Side A: 115 ÷ 215 = 53.49%.
- Side B: 105 ÷ 205 = 51.22%.
- Total = 104.71%. The overround is 4.71%.
- Divide each by the total: Side A = 53.49 ÷ 104.71 = 51.08%; Side B = 51.22 ÷ 104.71 = 48.92%.
The two fair probabilities now sum to 100%. Fair decimal odds are 1 ÷ 0.5108 = 1.958 for Side A and 1 ÷ 0.4892 = 2.044 for Side B, which are roughly -104 and +104 in American format.
Using the Fair Price to Evaluate Another Quote
Suppose a different sportsbook offers Side B at +110 (decimal 2.10). If you accept 48.92% as the fair chance, the expected value per unit is 0.4892 × 2.10 – 1 = +2.7%. If instead the quote were -105 (decimal 1.952), the expected value would be 0.4892 × 1.952 – 1 = -4.5%, the cost of the original margin. This is why comparing odds across sportsbooks matters: the difference between quotes is often larger than the difference between good and bad analysis. For a fuller treatment of the concept, see implied probability and expected value.
Keep in mind that a no-vig price is an estimate of the market’s opinion, not a certainty. A market can be wrong, and a single book’s number is only one data point.
Other Methods for Removing the Margin
The proportional method above (sometimes called the multiplicative method) is the easiest, and it assumes the margin is spread in proportion to each probability. Alternatives include:
- Additive method: subtract an equal share of the overround from each side.
- Power method: raise each implied probability to an exponent that makes the total 100%.
- Shin’s method: models the margin as a response to insider information.
For evenly matched two-way markets the methods produce very similar results. They diverge more for longshots, where bookmakers often load extra margin, so the proportional method can slightly overstate the chance of a heavy underdog.
Markets With Three or More Outcomes
The same process works for any number of outcomes. Convert every price to a probability, add them, and divide each by the sum. In a three-way soccer market (home, draw, away) the total is usually a few percentage points above 100%, and the fair probabilities are each outcome’s implied probability divided by that total.
A Quick Sanity Check With an Even-Money Market
Consider a market priced at -110 on both sides. Each side implies 110 ÷ 210 = 52.38%, so the total is 104.76% and the overround is 4.76%. Dividing each by the total gives 52.38 ÷ 104.76 = 50.00% for each side, which is exactly what you would expect from a symmetrical market. Fair odds are 2.00 (+100 in American format). This check is useful because if your calculation on a symmetrical market does not return 50/50, an error has crept in.
Notice too that the same -110 price costs bettors about 4.5% in expected value when the true chance is 50%, matching the overround of roughly 4.8% in scale. The smaller the overround, the closer the posted price is to fair, which is why low-margin markets are generally better for anyone comparing quotes.
One more practical point: recalculate whenever a price changes. Odds move as new information arrives, so a fair probability calculated in the morning may be stale by kickoff. Doing the arithmetic in a spreadsheet, with one row per market and columns for implied probability, total and fair probability, makes the process quick and repeatable, and reduces the chance of a slip.
Frequently Asked Questions
Is a no-vig price the “true” probability?
No. It is the market’s margin-free estimate, which is often informative but not perfect.
Why do some markets have more vig than others?
Prop bets, alternate lines, and low-liquidity markets typically carry larger margins than main lines in major leagues.
Can I bet at no-vig odds?
Generally not; the fair price is a benchmark. Some exchanges charge a commission instead of building a margin into the price.
Conclusion
To find fair odds, convert prices to probabilities, sum them, and normalise. In our example a -115 / -105 market implies a 4.71% overround and fair chances of 51.08% and 48.92%. With those numbers you can judge whether another quote is genuinely better, and you can see how margin builds up in products such as those described in parlay odds explained.
Educational content only, not betting advice. Please gamble responsibly; 21+ where applicable.