Selection | Real Odds | No Vig Odds |
---|---|---|

Selection 1 | Calculating... | |

Selection 2 | Calculating... | |

Total Book Percentage | 0.00% | 100% |

*The No Vig Calculator helps bettors determine the "fair" or "true" odds for a set of selections by removing the bookmaker’s margin (vig). To use it, input the real odds for each selection, and the calculator will show the No Vig odds and the implied probabilities, ensuring that the total book percentage is always 100%. This allows you to compare the bookmaker's odds with the fair market odds.*

## Detailed Instructions for Using the No Vig Calculator

- Enter Real Odds: In the "Real Odds" column, input the odds provided by the bookmaker for each selection. These odds represent the actual prices set by the bookmaker, which include their margin or vig.
- Add More Selections: If you need to add more selections, click the "Add Selection" button. Each new selection will allow you to input additional real odds, and the calculator will automatically update to reflect the new values.
- View Results:The "No Vig Odds" column will display the adjusted odds that represent the true probability of each outcome, removing the bookmaker’s margin.The "Real Book Percentage" shows the implied probability based on the bookmaker’s odds, while the "No Vig Book Percentage" always equals 100%, reflecting a fair market.

## What is No Vig?

The term "No Vig" refers to the calculation of "fair" odds by removing the bookmaker's margin, also known as the vig or overround. Bookmakers build their profit margin into the odds they offer, meaning that the sum of the implied probabilities of all possible outcomes usually exceeds 100%. By stripping out this margin, bettors can calculate the "true" or No Vig odds, which represent the actual probabilities of the outcomes without the bookmaker's profit built in.

### The Mathematics Behind No Vig

The core of No Vig calculations involves adjusting the bookmaker's implied probabilities so that their total sums to 100%. Here's how it's done:

- Implied Probability from Odds: The first step is to convert the bookmaker’s odds into implied probabilities. This is done using the formula:

\[ \text{Implied Probability} = \frac{1}{\text{Odds}} \]

For example, if the odds for a selection are 2.00, the implied probability is:

\[ \text{Implied Probability} = \frac{1}{2.00} = 0.50 \text{ or } 50\% \]

- Total Book Percentage: Summing the implied probabilities of all selections gives the total book percentage, which will usually be greater than 100% due to the bookmaker's margin.
- No Vig Odds Calculation: To calculate No Vig odds, we must adjust the implied probabilities so that they total exactly 100%. This is done by dividing each implied probability by the total book percentage:

\[ \text{No Vig Probability} = \frac{\text{Implied Probability}}{\text{Total Book Percentage}} \]

Finally, the No Vig odds are calculated by taking the inverse of the No Vig probability:

\[ \text{No Vig Odds} = \frac{1}{\text{No Vig Probability}} \]

### Real-World Example

Let’s say a bookmaker offers the following odds for a two-way market:

- Selection 1: Odds of 2.00
- Selection 2: Odds of 3.00

The implied probabilities are:

\[ \text{Selection 1: } \frac{1}{2.00} = 0.50 \text{ (50%)} \]

\[ \text{Selection 2: } \frac{1}{3.00} = 0.33 \text{ (33.33%)} \]

Total book percentage = 50% + 33.33% = 83.33%

The No Vig probabilities are calculated as:

\[ \text{Selection 1: } \frac{0.50}{0.8333} = 0.60 \]

\[ \text{Selection 2: } \frac{0.3333}{0.8333} = 0.40 \]

Finally, converting these probabilities back into No Vig odds:

\[ \text{Selection 1: } \frac{1}{0.60} = 1.67 \]

\[ \text{Selection 2: } \frac{1}{0.40} = 2.50 \]

So, the No Vig odds for Selection 1 and Selection 2 are 1.67 and 2.50, respectively, which represent the fair market odds.

### Issues with No Vig and the Favourite-Longshot Bias

While the No Vig calculation is designed to strip out the bookmaker’s margin and provide "fair" odds, it doesn’t always paint the full picture due to inherent biases in the betting market, particularly the favourite-longshot bias. This bias refers to the tendency for bookmakers to offer poorer prices on longshots over favourites compared to their real chance of winning.

As a result, No Vig calculations might not fully correct for this bias, especially in markets with extreme odds discrepancies. In practice, this means that while No Vig odds provide a more accurate reflection of probability, they may still skew slightly over-pricing favourites and under-pricing outsiders.

For example, in a horse race, a strong favourite might have odds of 1.50, while a longshot might have odds of 10.00. When calculating No Vig odds, the favourites's implied probability may be inflated. Bettors should be aware of this bias when using No Vig calculators, especially in markets with significant differences in odds, as it can affect the true value of the odds they are betting on.

## The History of No Vig in Gambling

The concept of No Vig has been crucial in the development of fair betting markets. In traditional betting, bookmakers build a margin into their odds to ensure profitability, often leading to less favorable odds for bettors. However, as betting exchanges such as Betfair emerged, where bettors could both back and lay selections directly, the need for calculating true market odds became more critical.

With betting exchanges, the concept of No Vig became popular as bettors sought to find the true value of bets, free from bookmaker bias. It has since become a common practice among professional bettors, especially in arbitrage, value betting, and sports trading, where minimising vig and maximising value is key to profitability. Today, No Vig calculations are an essential tool for anyone looking to place informed and value-driven bets.

## Conclusion

By calculating No Vig odds, bettors can strip out the bookmaker's margin and evaluate the real probabilities of outcomes, ensuring they are getting the fairest possible price. However, it's important to keep in mind that market biases like the favourite-longshot bias can still influence odds, even after the vig is removed. This makes understanding both the maths and market dynamics critical to using No Vig calculations effectively.