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Vig Free Odds Calculator

This free calculator removes the proportional vig from two opposing selections in the same two-outcome market. Enter both listed prices to estimate normalized fair probabilities and vig-free American and decimal odds.

Calculate vig-free odds

Load an example: Two sides at -110 · -150 favorite and +130 underdog

Fair odds estimate

Total original implied probability: 104.7619%
Signed overround · Overround: +4.7619%

Proportional normalization of the two quoted prices
Selection	Original implied probability	Vig-free probability	Fair American odds	Fair decimal odds
Side 1	52.3810%	50.0000%	+100	2.00
Side 2	52.3810%	50.0000%	+100	2.00

Fair odds are normalized market-price estimates, not independently verified true winning probabilities. Removing margin does not guarantee profit.

Overround: the quoted implied probabilities total more than 100%. This is not the sportsbook's realized hold or profit.

How to use the calculator

Choose American or decimal format, then enter the two opposing prices exactly as listed.
Confirm both selections belong to the same two-outcome market and use the same settlement rules.
Calculate to compare each original implied probability with its proportional vig-free estimate.
Share or bookmark the generated GET URL; its format, odds1, and odds2 parameters reproduce the calculation without JavaScript.

Method: proportional normalization

1. Convert each price

For positive American odds A, p = 100 / (A + 100). For negative American odds A, p = |A| / (|A| + 100). For decimal odds D, p = 1 / D.

2. Measure the market sum

Let S = p1 + p2. The quoted overround is (S - 1) × 100%. Positive values are overround, zero is fair, and negative values are underround.

3. Normalize proportionally

The fair estimates are q1 = p1 / S and q2 = p2 / S, so the two fair probabilities are complementary and sum to 1.

4. Convert the fair estimates back to odds

Fair decimal odds are 1 / q. For American odds: when q < .5 use +100 × (1 - q) / q; when q > .5 use -100 × q / (1 - q); and when q = .5 use +100.

Worked examples

Two sides at -110

Each -110 price implies 52.3810%, for a 104.7619% sum and +4.7619% overround. Normalizing gives 50.0000% per side, fair decimal odds of 2.00, and fair American odds of +100.

Calculate this example

-150 favorite and +130 underdog

-150 implies 60.0000% and +130 implies 43.4783%, for a 103.4783% sum and +3.4783% overround. The proportional fair estimates are 57.9832% and 42.0168%, fair decimal odds 1.72 and 2.38, and fair American odds -138 and +138.

Calculate this example

Definitions

Vig: Short for vigorish: the bookmaker's margin reflected in quoted prices. This calculator measures the two-price overround and removes it proportionally, not as a claim about realized hold or profit.
Implied probability: The probability encoded by one listed price before the margin is removed. It is a price conversion, not an independently verified forecast.
Overround: The amount by which the two implied probabilities sum above 100%. It describes this quoted market and is not the sportsbook's realized hold or profit.
Underround: A negative overround: the two listed implied probabilities sum below 100%. It is not, by itself, an arbitrage finding or a guarantee of realized profit.
Vig-free probability: An estimate produced by dividing each implied probability by their sum. The proportional method assumes the same scaling for both sides and makes no favorite/longshot adjustment.
Fair odds: American or decimal prices corresponding to the normalized vig-free probabilities. They are a fair odds estimate under the proportional method, not independently verified true winning probabilities.

Assumptions and limitations

Use only two opposing selections in the same two-outcome market with identical settlement rules.

Three-way markets are excluded, including soccer markets with a draw outcome.

Push probability is not modeled; estimates are conditional on a non-push and require matching push treatment.

The outputs are price-derived estimates, not independently verified true probabilities or guaranteed profit.

Overround is not realized sportsbook hold, and underround is not automatically an arbitrage opportunity.

Proportional normalization assumes equal scaling across both sides and does not adjust for favorite/longshot bias.

Inputs use plain finite numbers. American odds must be at most -100 or at least +100; decimal odds must exceed 1; maximum absolute raw odds are Number.MAX_SAFE_INTEGER (9,007,199,254,740,991).

Calculations retain double precision, while probability and overround displays round to four decimals, decimal odds to two, and American odds to the nearest whole number. Tiny boundary values use honest bounds rather than false 0% or 100% endpoints.

Frequently asked questions

What does a vig-free odds calculator do?

It converts both prices to implied probabilities and proportionally normalizes them to 100%, producing estimated fair probabilities and equivalent fair odds.

Can I use prices from different markets or sportsbooks?

Only use opposing selections from the same two-outcome market with matching settlement rules. Mixing lines, scopes, or settlement terms does not represent one market sum.

Does this calculator support three-way soccer markets?

No. It excludes three-way markets, including soccer markets where a draw is a separate outcome. All mutually exclusive outcomes must be included in a margin calculation.

How are pushes handled?

A push is not modeled. Results are conditional on a non-push outcome, so only compare prices with the same push and settlement treatment.

Are vig-free probabilities the true probabilities?

No. They are proportional estimates derived from quoted prices, not independently verified true probabilities, and they do not guarantee profit.

Is overround the same as sportsbook hold?

No. Overround is calculated from quoted prices. Realized hold depends on stakes, outcomes, timing, limits, voids, and settlement.

What odds and URL formats are supported?

Plain American prices at or beyond -100 or +100 and decimal prices greater than 1 are supported up to 9,007,199,254,740,991 in absolute value. GET URLs use format, odds1, and odds2; a literal plus sign must be percent-encoded as %2B.

Calculation URLs and no-JavaScript use

The canonical calculator path is /vig-free-odds-calculator.

Use GET parameters in the order format, odds1, and odds2. Supported format values are american and decimal.

Percent-encode reserved characters. In a query string, a literal + in American odds must be encoded as %2B because an unescaped + is decoded as a space.

The URL stores exact input text without calculation rounding and can be evaluated in the server-rendered, no-JavaScript response.