While the NFL point spread is the most popular type of bet in the

United States, most that bet this proposition are unfamiliar with how

to calculate the point spread odds themselves, and this article aims to

change that.

Because of the way football is scored, some point spreads are

more important than others. As such, it is worth the time to read the

article on Key NFL Point Spreads before continuing.

**The Team's Winning Percentage is Everything**

Before you can calculate point spread odds you must have an idea as to

how often the teams playing in the game are going to win. This is the

most crucial part to calculating fair point spread odds, as the actual

margin of victory in a game is a chance event. The more often a team

wins the game the more likely they are to win by a larger margin of

victory. To calculate how often you can expect at team to win, checkout

Smart Pro Football Handicapping.

Once you know a team's probability of winning a given game, you can

then calculate the probability of the team covering a specific point

spread.

To calculate these point spread odds you must know the

**conditional probability distribution**for a team winning by a specific number of points given that

**we already know they have won**

the game. This distribution for the average NFL game is referred to as

the overall margin of victory distribution and is shown below.

**Overall Margin of Victory Distribution**

For an average NFL game the winning team's margin of victory will follow the following probability distribution:

Margin of Victory | Exactly | Less Than | Greater Than | Less Than or Equal To |
---|---|---|---|---|

1 | 3.46% | 0.00% | 94.60% | 3.46% |

2 | 2.89% | 3.46% | 90.57% | 6.85% |

3 | 14.51% | 6.85% | 73.69% | 22.29% |

4 | 3.39% | 22.29% | 69.31% | 26.45% |

5 | 2.64% | 26.45% | 65.81% | 29.82% |

6 | 4.18% | 29.82% | 60.58% | 34.89% |

7 | 8.08% | 34.89% | 51.13% | 44.19% |

8 | 2.57% | 44.19% | 47.78% | 47.54% |

9 | 1.14% | 47.54% | 46.10% | 49.21% |

10 | 5.12% | 49.21% | 39.94% | 55.43% |

11 | 2.19% | 55.43% | 37.06% | 58.36% |

12 | 1.01% | 58.36% | 35.56% | 59.90% |

13 | 2.64% | 59.90% | 32.17% | 63.38% |

14 | 3.68% | 63.38% | 27.66% | 68.05% |

15 | 0.85% | 68.05% | 26.37% | 69.39% |

16 | 1.40% | 69.39% | 24.43% | 71.43% |

17 | 2.93% | 71.43% | 20.78% | 75.29% |

18 | 1.61% | 75.29% | 18.62% | 77.59% |

19 | 0.75% | 77.59% | 17.46% | 78.83% |

20 | 1.40% | 78.83% | 15.54% | 80.90% |

21 | 2.02% | 80.90% | 12.95% | 83.74% |

To account for a margin of error, the data in the table above are

the lower limits of a one-sided 99% confidence interval based on actual

results for NFL regular season games from the 1997-2006 seasons.

**A Quick Word Regarding Blowouts**

A common mistake NFL point spread bettors make is betting on the blowout.

Based on the data in the table above you can see that at least

27.66% of all NFL games will end with a margin of victory of 15 points

or higher. It's easy to see why bettors bet for the blowout, as that's

roughly 1 out of every 4 games!

Bettors hate to see their team get crushed, but like it or

not, at least 12.95% of all games will have the winning team do so by

22 or more points (almost 1 out of every 8 games).

Don't let these probabilities affect you psychologically when

looking over a given Sunday's results. Your bankroll will thank you for

it.

**The Home and Away Difference**

Only a very small percentage of NFL games are played at a

neutral site, so it is important to take into account the difference

between winning at home and winning on the road when calculating point

spread odds.

**Home Margin of Victory Distribution**

Margin of Victory | Exactly | Less Than | Greater Than | Less Than or Equal To |
---|---|---|---|---|

1 | 2.94% | 0.00% | 94.58% | 2.94% |

2 | 2.36% | 2.94% | 90.84% | 5.90% |

3 | 13.24% | 5.90% | 74.55% | 20.27% |

4 | 2.82% | 20.27% | 70.51% | 24.03% |

5 | 2.36% | 24.03% | 67.06% | 27.29% |

6 | 3.06% | 27.29% | 62.78% | 31.37% |

7 | 7.70% | 31.37% | 53.28% | 40.62% |

8 | 2.24% | 40.62% | 50.04% | 43.81% |

9 | 0.97% | 43.81% | 48.39% | 45.45% |

10 | 4.74% | 45.45% | 42.31% | 51.56% |

11 | 2.07% | 51.56% | 39.33% | 54.59% |

12 | 0.92% | 54.59% | 37.77% | 56.18% |

13 | 2.47% | 56.18% | 34.33% | 59.72% |

14 | 3.29% | 59.72% | 29.96% | 64.25% |

15 | 0.47% | 64.25% | 29.03% | 65.23% |

16 | 1.29% | 65.23% | 27.02% | 67.34% |

17 | 3.06% | 67.34% | 22.98% | 71.64% |

18 | 1.51% | 71.64% | 20.73% | 74.05% |

19 | 0.76% | 74.05% | 19.42% | 75.48% |

20 | 1.40% | 75.48% | 17.33% | 77.76% |

21 | 1.57% | 77.76% | 15.05% | 80.28% |

**Away Margin of Victory Distribution**

Margin of Victory | Exactly | Less Than | Greater Than | Less Than or Equal To |
---|---|---|---|---|

1 | 3.38% | 0.00% | 93.45% | 3.38% |

2 | 2.89% | 3.38% | 88.74% | 7.05% |

3 | 14.68% | 7.05% | 70.38% | 23.19% |

4 | 3.38% | 23.19% | 65.45% | 27.80% |

5 | 2.34% | 27.80% | 61.83% | 31.23% |

6 | 4.85% | 31.23% | 55.23% | 37.60% |

7 | 7.39% | 37.60% | 45.84% | 46.88% |

8 | 2.34% | 46.88% | 42.32% | 50.42% |

9 | 0.92% | 50.42% | 40.62% | 52.15% |

10 | 4.69% | 52.15% | 34.41% | 58.53% |

11 | 1.73% | 58.53% | 31.70% | 61.35% |

12 | 0.72% | 61.35% | 30.30% | 62.81% |

13 | 2.19% | 62.81% | 27.06% | 66.24% |

14 | 3.38% | 66.24% | 22.46% | 71.17% |

15 | 0.99% | 71.17% | 20.73% | 73.06% |

16 | 1.06% | 73.06% | 18.91% | 75.06% |

17 | 2.03% | 75.06% | 15.93% | 78.37% |

18 | 1.21% | 78.37% | 13.96% | 80.60% |

19 | 0.40% | 80.60% | 13.07% | 81.61% |

20 | 0.92% | 81.61% | 11.48% | 83.45% |

21 | 2.03% | 83.45% | 8.60% | 86.86% |

The important thing to remember about the difference between

winning at home versus winning on the road is that teams that win at

home are more likely to win by a larger margin than teams that win on

the road.

With this key difference in mind, you've not got all the data you need to calculate point spread odds.

**Calculating the Odds**

With winning probabilities and margin of victory distributions in hand you can now calculate point spread odds.

Below are a couple of examples.

**Example #1**: You approximate the true winning percentage for a

team playing at home to be 58%, and the listed point spread is home

team -3 points. What are the fair odds for the home team covering -3

points and the away team covering +3 points?

**Probability of home team covering -3 points**:

Using the home team margin of victory distribution, when the

home team wins they will do so by more than 3 points at least 74.55% of

the time, and they will win by exactly 3 points at least 13.24% of the

time. You can use this data to calculate the fair point spread odds as

follows:

The top portion of this calculation calculates the probability that

the home team will win by more than 3 points. This result is then

divided by the probability that the home team does not win by exactly 3

points, as ties do not count as a win or a loss. As such, the final

probability of the home team covering -3 points is 46.84%. Using a money line converter, this equates to fair odds of +113.

**Probability of away team covering +3 points**:

Again, using the home team margin of victory distribution, when the

home team wins they will do so by less than 3 points at least 5.90% of

the time, and they will win by exactly 3 points at least 13.24% of the

time. You can use this data to calculate the fair point spread odds as

follows:

The top portion of this calculation calculates the probability that

the home team will win by 2 points or less combined with the

probability that the away team will win outright. This result is then

divided by the probability that the home team does not win by exactly 3

points, as ties do not count as a win or a loss. As such, the final

probability of the away team covering +3 points is 49.20%. Using a money line converter, this equates to fair odds of +103.

It should now be obvious that the probabilities calculated above do not

sum to 100%. The "left over" 3.96% (100% - 46.84% - 49.20% = 3.96%) is

due to the margin of error. Because we're using historical data, we

can't be 100% sure of the exact probabilities.

**Example #2**: You approximate the true winning percentage for a

team playing on the road to be 75%, and the listed point spread is away

team -4.5 points. What are the fair odds for the away team covering

-4.5 points and the home team covering +4.5 points?

**Probability of away team covering -4.5 points**:

Using the away team margin of victory distribution, when the

away team wins they will do so by more than 4 points at least 65.45% of

the time. You can use this data to calculate the fair point spread odds

as follows:

As this calculation shows, the probability of the away team covering -4.5 points is 49.09%. Using a money line converter, this equates to fair odds of +104.

**Probability of home team covering +4.5 points**:

Again, using the away team margin of victory distribution, when

the away team wins they will do so by less than or equal to 4 points at

least 27.80% of the time. You can use this data to calculate the fair

point spread odds as follows:

As this calculation shows, the probability of the home team covering +4.5 points is 45.85%. Using a money line converter, this equates to fair odds of +118.

As with the first example, it should now be obvious that the

probabilities calculated above do not sum to 100%. Again, the "left

over" 5.06% (100% - 49.09% - 45.85% = 5.06%) is due to the margin of

error.

**Summary**

Using the data and calculations provided in this article you

should now be able to calculate point spread odds for any National

Football League game.

## No comments:

## Post a Comment