How to use this betting tool
- Enter two-way market values using the units shown.
- Select any settlement option that applies.
- Choose Calculate and review the primary result plus the supporting breakdown.
- Use Reset before evaluating a separate scenario.
#031 · Odds Probability & Margin Tool
Vig Distribution Calculator
See how a two-way market’s overround is distributed across its outcomes. Enter decimal odds to separate quoted implied probability from a proportional no-vig estimate.
Calculator
Two-way marketdecimal
decimal
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What this tool calculates
The calculator measures a two-outcome market’s overround and removes it using proportional normalization. This is a mathematical estimate, not a claim about the bookmaker’s actual pricing model.
Raw probability = 100 ÷ decimal odds. Fair probability = raw probability ÷ total raw probability × 100. Overround = total raw probability − 100%.
Results use the assumptions shown on this page. Actual settlement may differ under operator, jurisdiction, or market-specific rules.
Worked example
At decimal odds of 1.91 on both outcomes, each raw implied probability is about 52.356%. The total is 104.712%, so the overround is about 4.712% and each proportional fair probability is 50%.
| Input | Value |
|---|---|
| Outcome A / B odds | 1.91 / 1.91 |
| Overround | 4.712% |
| Fair probabilities | 50% / 50% |
Tips and limitations
- Use decimal odds from the same market and settlement period.
- Keep unrounded inputs; rounding is applied only to displayed results.
- Check operator rules for voids, deductions, overtime, limits, or special settlement.
- This is informational betting math, not a recommendation or a prediction.
FAQ
How is vig distributed in a two-way market?
This tool normalizes each raw implied probability by their combined total, so the margin is allocated in proportion to the quoted probabilities.
Does proportional no-vig removal reveal true probability?
No. It produces a coherent fair-probability estimate but cannot reveal the bookmaker’s private model or unequal margin policy.
Why can the two implied probabilities exceed 100%?
The amount above 100% is the market overround, commonly used as a visible measure of bookmaker margin.
Can I use odds below 1.01?
Decimal odds must be greater than 1.00. Extremely short odds are accepted only within the page’s stated input limit.
What if the implied total is below 100%?
That is an underround rather than positive vig, so this calculator reports an error instead of describing it as bookmaker margin.
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Calculation reference
| Item | Definition |
|---|---|
| Input format | Two-way market |
| Primary output | Market overround |
| Precision | Full internal precision; display rounded for readability |
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