Try Calculating Your "OWN" Football Lines Before they Come Out

[Kramer]

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
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.
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

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.


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:



As this calculation shows, the probability of the home team covering +4.5 points is 45.85%. , 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.


Favorite: -3 53.64%cover % -116odds 1.8621decimal odds, 10/11.6fractional odds
Underdog: +3 46.36%cover % +116 ,2.1600 dec odds ,11.6/10 frac odds

THE MEASURE OF SUCCESS OF A SPORTS HANDICAPPER IS NOT HIS PERCENTAGE OF WINNING BETS,
BUT THE RELATING AMOUNT OF PROFIT HE MADE OVER ANY GIVEN PERIOD OF TIME.

If you don't know the winning % chance of the team you're betting on ,
then it basicaly a coin flip ...

GL

[jaxul]

tks for post