What does a no-vig calculator do?
A no-vig calculator removes the bookmaker’s margin from a complete set of odds. It gives fair odds and market-implied probabilities using proportional normalization.
- Inputs
- Decimal or American odds, 2–10 outcomes
- Method
- Proportional normalization
- Privacy
- Calculations stay in your browser
Key points
- Use all mutually exclusive outcomes from the same market, including a draw when it is possible
- Read overround as the excess implied probability above 100%, not a guaranteed bookmaker profit rate
- Compare the no-vig estimate with a prediction-market price only after checking fees, liquidity, and settlement rules
Method and assumptions
The no-vig formula
For decimal odds d, implied probability is 1 ÷ d. Add these probabilities across every outcome to get the book total S. Fair probability for outcome i is (1 ÷ dᵢ) ÷ S; fair decimal odds are 1 ÷ fair probability. Overround is (S − 1) × 100%. This proportional method preserves the ratio between the original implied probabilities.
- Convert every outcome to decimal odds.
- Sum the implied probabilities: S = Σ(1 ÷ d).
- Divide each implied probability by S.
- Invert each normalized probability to get fair decimal odds.
Example: 1.91 on both sides
Two outcomes priced at 1.91 each imply 52.36% per outcome, or 104.71% in total. The overround is 4.71%. Dividing each implied probability by the total gives 50% per outcome: fair decimal odds of 2.00, or American odds of +100. Values shown are rounded; calculations use full precision.
Compare with a prediction-market price
A no-vig estimate of 60% corresponds to a reference price of $0.60 for a contract that pays $1 if the outcome occurs. It is a comparison point, not a recommendation to trade. Match the exact event and resolution rules, then account for fees, the bid–ask spread, and slippage before evaluating any difference.
- Use odds from the same source and time to estimate that market’s margin.
- Do not omit the draw or other possible outcomes.
- Prices from multiple venues can have different resolution and execution conditions.
Assumptions and limits
The model assumes a complete set of mutually exclusive outcomes and allocates margin proportionally. It does not adjust for favorite–longshot bias, model push or void probabilities separately, or establish a true probability. Other methods of removing vig can produce different estimates.
- Decimal inputs must be greater than 1 and no more than 1,000,000.
- American inputs must be at least +100 or at most −100 and convert into the supported decimal range.
- Totals below 100% are flagged as underround. Missing outcomes or stale quotes can cause this; it is not proof of executable arbitrage.
- Unrounded probabilities sum to 100%; displayed values can differ slightly because of rounding.
Frequently asked questions
What is vig or overround?
Vig is the bookmaker’s pricing margin. This tool measures overround: the sum of implied probabilities minus 100%. It is not the same as realized bookmaker profit or a trading fee.
Does removing vig reveal the true probability?
No. Proportional normalization gives a market-derived estimate based on the entered odds and an assumption about how margin is distributed. The market can still be wrong.
Can I use it for a three-way market?
Yes. Add an outcome for the draw or another possible result. Include all mutually exclusive outcomes. The calculator supports up to ten.
Which odds formats are supported?
Decimal and American odds. Switching formats converts valid entries. Incomplete or invalid entries are cleared so they can be re-entered in the new format.
What if the implied probabilities total less than 100%?
The calculator shows an underround warning and still normalizes the inputs. First check for missing outcomes, stale odds, and different settlement rules. Execution costs and available liquidity also matter.
Is this different from an odds converter?
An odds converter translates one quote between formats. A no-vig calculator uses all outcomes in a market to remove its overround before showing normalized probabilities and fair odds.