Free mixed-format market tool
Betting margin, overround and no-vig calculator
Enter every mutually exclusive outcome from the same market snapshot. The calculator converts mixed regional odds, totals their implied probabilities and shows the book percentage, overround, inverse-overround payout estimate and normalized fair prices. It does not fetch live Luckly.gg odds, identify value or predict a result.
Margin estimate from 2 outcomes
| Outcome | Decimal | Quoted implied | Normalized no-vig | Fair decimal |
|---|---|---|---|---|
| Side A | 1.91 | 52.36% | 49.99% | 2.00 |
| Side B | 1.909 | 52.38% | 50.01% | 2.00 |
“No-vig” here means proportional normalization under an equal-margin assumption. The normalized outputs are not objective true probabilities, a positive edge or an expected result.
How the book percentage and payout estimate differ
First convert each outcome to decimal odds. Its quoted implied probability is one divided by that decimal price. Add every probability from the complete market to get the book total. A fair book totals 100%; a total above 100% is commonly called the overround. Dividing 100 by the book percentage gives the conventional equal-margin payout estimate, and subtracting that value from 100 gives the corresponding margin estimate.
| Measure | Formula | Two prices at 1.90 |
|---|---|---|
| Book percentage | Σ (100 ÷ decimal odds) | 105.26% |
| Overround | Book percentage − 100 | 5.26 points |
| Payout estimate | 100 ÷ book total | 95.00% |
| Margin estimate | 100 − payout estimate | 5.00% |
| Normalized probability | Outcome implied % ÷ book total | 50.00% each |
Use one complete market snapshot
Enter all outcomes that can settle as the winner of the same market: both sides of a two-way moneyline, Home/Draw/Away for a three-way match result, or every listed runner for an outright. Do not mix a match winner with a handicap, prices captured at different times, or best prices collected from several sportsbooks. Those figures do not represent one quoted book and can create an apparent underround or distorted total.
- Copy the exact displayed price and format from the same market screen.
- Include every mutually exclusive outcome that completes that market.
- Recalculate after a price move, suspension, void or market-rule change.
- Treat normalized prices as a comparison baseline, not a prediction or tip.
- Never increase a stake because a calculated margin appears low.
The estimate has an important research limitation
University College Dublin researchers describe the inverse-overround method as a conventional estimate that assumes equal expected margins across outcomes. Their soccer and tennis evidence shows that favorite-longshot bias can make realized average losses higher than the formula suggests. This calculator therefore labels the result as an estimate and never presents it as a guaranteed loss rate or true probability.
Method and limitation source: Hegarty and Whelan, University College Dublin, “Calculating The Bookmaker's Margin,” equations 1–2 and conclusions. Format source: CGMBet System User Guide, odds-converter sections 16.8–16.9.
Betting margin calculator questions
What is the difference between book percentage and overround?
Book percentage is the sum of every outcome's implied probability. Overround is the amount above 100 percentage points. A 105% book therefore has a 5-point overround.
Is overround the same as the bookmaker's profit margin?
Not exactly. A common equal-margin estimate of payout is 100 divided by the book percentage; the corresponding margin estimate is 100 minus that payout. Overround and this estimate are close at small margins but are not identical.
Are normalized no-vig probabilities the true probabilities?
No. Dividing each implied probability by the book total removes the overround proportionally. It is a transparent equal-margin baseline, not an independent forecast or proof of value.
Why must every outcome come from the same market snapshot?
A book total is meaningful only when the prices cover all mutually exclusive outcomes from one market at the same time. Mixing bookmakers, times, lines or incomplete outcomes can produce a misleading result.
Does this calculator use live Luckly.gg prices?
No. It performs arithmetic only on the figures entered. It does not fetch a Luckly.gg market, confirm availability, reproduce a betslip or recommend a selection.