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How To Calculate NFL Point Spread Odds

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.

Key NFL Point Spreads

Because of the way football games are scored, some point spreads are more important than others. These point spreads are commonly referred to as the key point spreads.

These key point spreads are: 3, 7, 10, and 6.

To understand why these point spreads are important, you must take a look at the NFL's margin of victory distribution:


The graphic above shows the relative frequencies for the specified margins of victory for regular season games during the 2002-2003 through 2006-2007 NFL seasons.

The numbers 3, 7, 10, and 6 are key because they make up 38% of all margins of victory in the NFL.

The number 3 is the most important as it has a relative frequency of 16.26%. The number 7 is next on the list with a relative frequency of 9.77%, which makes the number 3 a little over 1.5 times as important as the number 7. The number 10 has a 6.57% relative frequency, and the number 6 has a 5.79% relative frequency. This makes the number 3 about 2.5 times as important as the number 10 and 2.8 times as important as the number 6. As such, when you're looking to place a bet on a team to cover the point spread, always ensure you're getting the best number possible, especially if the point spread is one of the key numbers.

The Difference between Playing at Home and Away

When handicapping a game you will want to separate the home and away distributions, as some numbers are slightly more important for a visiting team than they are for a home team.

Pictured below is the margin of victory distribution when the home team wins:


When the home team wins, the relative frequencies for the key point spreads are as follows: 15.45% for the number 3; 10.43% for the number 7; 6.78% for the number 10; and 4.89% for the number 6. Another thing to note about this distribution is that the number 14 is almost as important as the number 6, as it has a relative frequency of 4.61%. (This is a moot point, however, as you should rarely lay 14 points in the NFL; so rare, in fact, that it's best to never consider laying 14 points.)

For visiting teams, however, these key point spreads mean a little more than they do for teams playing at home.

Pictured below is the margin of victory distribution when the away team wins:


When the away team wins, the relative frequencies for the key point spreads are as follows: 17.38% for the number 3; 8.87% for the number 7; 7.02% for the number 6; and 6.28% for the number 10. Based on this data, the number 6 is slightly more important than the number 10 when betting visiting teams.

It's also worth nothing that the number 4 is important as well, as it has a relative frequency of 5.36%. The number 14 is again almost as important when a relative frequency of 5.18%, but again, it's best to never consider laying 14 points, so it isn't worth taking into consideration when placing a bet.

Always Shop

Now that you know the relative importance of key point spreads in the NFL, it is imperative to always shop for the best number, regardless of the point spread. That said, getting a better number than one of the key point spreads will provide you with the most benefit.