Calculate no-vig fair odds and probabilities from decimal or American odds for a two-way or 3-way market, and see the vig built into the line.
No Vig Formula and Method
Raw implied fraction = 1 / odds
List every outcome of a single market, using decimal prices for selections that cannot win together and cover all possible results. Their reciprocal prices are raw implied fractions. The overround is their sum minus one, expressed in percentage points.
How to Use This Calculator
Enter decimal odds for all mutually exclusive outcomes of one complete market, then select Calculate. Use 2–20 prices from 1.000001 to 10,000, separated by commas, spaces, new lines or semicolons. The result shows the overround and each outcome’s proportionally normalized probability and fair decimal odds.
Worked Example
For decimal odds of 1.91 and 1.91, each raw implied probability is 1/1.91 ≈ 52.3560%. Their total is 104.7120%, so the overround is 4.7120 percentage points above 100% (often written as 4.7120%). Dividing each raw fraction by the total gives 50.0000% and fair decimal odds of 2.000000 for each outcome.
Normalized fraction = raw fraction / sum of all raw fractions
Input and Example Guide
| Input or category | Example or weight | Entry guidance |
|---|---|---|
| Every outcome price (decimal odds) | 1.91, 1.91 | Enter every outcome of the same complete market, using matching settlement rules. |
| Outcome 1 normalized probability / fair odds | 50% / 2 | Calculated for the entered example. |
| Outcome 2 normalized probability / fair odds | 50% / 2 | Calculated for the entered example. |
Interpreting the Result
Proportional normalization divides each raw fraction by the total. This makes the adjusted fractions add to one and gives reciprocal normalized prices. It is one mathematical margin-removal convention. It does not correct favorite–longshot bias, account for missing markets or establish the true chance of a selection.
This removes margin proportionally. It is not a model of true probabilities or an adjustment for favorite–longshot bias; enter every mutually exclusive outcome.
Assumptions and Common Input Errors
Use matching settlement rules for every price. Missing outcomes, duplicate selections and mixed markets invalidate the interpretation. Commission and tie-payout adjustments are excluded. A negative overround is an underround, and the same proportional normalization still applies. Unrounded normalized probabilities sum to 100%; displayed probabilities may differ slightly because of rounding. This mathematical convention does not establish actual chances or a guaranteed profit rate.
Saving and Revising a Scenario
A successful calculation is saved in this browser and can be restored on the next visit. Restored results are labeled with their saved time. Editing the odds keeps the previous result visible with an inputs-changed status until Calculate updates it. Reset clears the odds and this calculator’s saved data. Other scripts on this site may access browser storage.
Sources
Smarkets: decimal odds and implied probability; Smarkets: betting margins and overround; Jonas C. Lindstrøm: the basic normalization method in the implied package. The calculator uses that proportional arithmetic convention, without treating its normalized values as established actual chances.
