Free iGaming research tool
Overround calculator
Enter a complete market to calculate its overround, proportional hold and normalized probabilities. Mix decimal, American and fractional formats. Keep the result as a CSV.
Overround calculator
Load an example, or enter every outcome in one market.
Include the draw in a three-way market. Use one bookmaker, market, line, period and observation time. A missing outcome changes the result.
Your calculation
Overround
4.71pp
Percentage points above a 100% book.
- Book percentage
- 104.71%
- Proportional hold
- 4.50%
| Outcome | Implied | No-vig | Decimal |
|---|---|---|---|
| Home | 52.36% | 50.00% | 2.000 |
| Away | 52.36% | 50.00% | 2.000 |
“No-vig” divides each implied probability by their sum. It is a proportional model, not an estimate of the true chance. Hold here is theoretical under that model, not the bookmaker's measured profit.
Overround and hold measure different things
For each decimal price d, the implied probability is 1/d. Add every outcome to get the book B. Overround is B − 1, expressed here in percentage points. Proportional hold is (B − 1)/B. The normalized probability for an outcome is (1/d)/B.
B = Σ(1 / decimal odds)
Overround = (B − 1) × 100 pp
Proportional hold = (B − 1) / B × 100%
Worked example: 1.91 on both sides
Two mutually exclusive, exhaustive outcomes at 1.91 each imply 52.36% each. The book is 104.71%, the overround is 4.71 percentage points, and proportional hold is 4.50%. Dividing each implied probability by the book gives 50% each, equivalent to 2.00 decimal odds. This example is illustrative.
When this comparison breaks
A football market with a draw needs three outcomes. A regulation-time market differs from one that includes overtime. A two-way draw-no-bet market has a possible refund, so its unconditional outcome probabilities need a separate push model. This calculator assumes exactly one listed outcome wins and no other settlement applies.
Quotes from different times, bookmakers or handicap lines are not one bookmaker's book. Taxes, exchange commission, stake limits, voids, deductions and the ability to place a bet are outside this calculation. A positive overround does not reveal the margin on each outcome or actual profit.
Does removing the vig reveal the true probability?
No. Proportional normalization allocates the excess in proportion to the quoted implied probabilities. Other methods allocate it differently. Use the result as an explicitly defined comparison baseline, then test calibration against outcomes and the market's settlement rules.