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Using historical NFL margin of victory data you can approximate fair money line odds for a given NFL point spread, and this article provides you with a method for doing just that.
It is worth noting, however, that because of the fact that some point spreads are worth more than others, the money line you derive using the formula below must be entered
into an NFL point spread calculator to calculate the fair point spread odds for that specific money line.
As a quick reference you can use this point spread to money line conversion chart. This chart provides you with a list of various point spread odds and their associated money line odds.
Also, checkout the NFL point spread to money line converter to perform these calculations for you.
Understanding the Historical Margin of Victory Data
The first step to converting an NFL point spread to a money line is to use historical data to understand the relationship between the margin of victory and the team's probability of winning the game.
To derive the relationship between margin of victory and probability of winning you must know two things: 1) the probability of the home team winning and 2) the average margin of victory.
Using 10 years of NFL regular season data from the 1997 to 2006 seasons, this information can be derived as follows:
During this time period, ignoring ties, home teams won 58.22% by an average margin of victory of 2.7 points.
To derive the point spread to money line conversion formula we can use 58.22% as the probability of the home team winning, but we can't use an average margin of victory of 2.7 points. This is because 2.7 isn't the number that evenly divides 50% of the probabilities of the distribution, which is what we must use to perform the calculation.
Based on the data, the true number that evenly divides 50% of the probabilities is 2.43722, so this is what we will use to convert point spreads to money lines.
Deriving the Conversion Factor
So far we know that 58.22% represents the probability of the home team winning, and 2.43722 represents the true average margin of victory. Using this data we can now calculate the conversion factor that will be used to convert point spreads to money lines.
Because we know the true mean is 2.43722 and winning percentage is 58.22%, the equation for calculating the conversion factor can be setup as follows:
Solving for the conversion factor in this equation we obtain:
Using this conversion factor we can now obtain formulas for converting a point spread to a money line and for converting a money line to a point spread.
Point Spread to Money Line Conversion Formula
With a conversion factor of 29.64988, the formula for converting a point spread to a money line is:
Note: You should ensure that the minimum and maximum winning percentages calculated with this formula are 0% and 100%, respectively. Percentages below 0% or above 100% indicate an unfair point spread, so you should instead use 0% or 100% as the fair winning percentage. Also, a negative point spread indicates the team is an underdog.
After using this formula to calculate a fair winning percentage you can then convert this percentage to a money line using a money line converter.
Money Line to Point Spread Conversion Formula
To convert a money line to a point spread you must first use a money line converter to convert the money line to a winning percentage. With the winning percentage in hand, you can use the following formula to calculate the point spread:
Note: This formula assumes that the winning percentage is represented as a number from 0 to 1. Also, a negative result indicates the team is an underdog.
This point spread value can then be rounded to the fair point spread value. For example, you use this formula and calculate a point spread value of 4.21. This value is closer to 4 than it is to 4.5, so you can say the fair point spread is 4.
Factoring in Key Point Spreads
Because of the key NFL point spreads, you will need to use an
NFL point spread calculator to calculate the fair point spread odds for the point spread value obtained from the formula above.
See the point spread to money line conversion chart for a quick reference to these fair odds.
Summary
Using the formulas provided in this article you should now be able to convert a point spread to a money line, and vice-versa, for any NFL football game.
- Ryan J. Parker | Ryan's sports betting blog
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