When it comes to NFL betting systems, the Point Differential System is one of the most time-consuming, but also one of the most accurate when trying to gauge the relative offensive and defensive strength of a particular team.

The system incorporates the strength of the opposition the team has played, which makes it a bit more accurate than basing a team's performance against the league average or the league median.

If a team is averaging 24 points a game, that doesn't really tell us too much unless we have something to base that against. The most common base is the league average or league median. If the average NFL team scores 21.6 points per game, we can now rank our team scoring 24 points a game as a better-than-average offensive team.

The one problem with this, however, is that it fails to take the defensive strength of the team's opposition into consideration. If our team averaging 24 points per game has played against opponents who allow an average of 27 points per game, our ranking of them as a better-than-average offensive team will be misleading. Instead of being a good offensive squad, the team is actually scoring three points less than they should, based on the opposition they have played.

That's where the NFL Point Differential System comes into play.

### Doing the System Calculations

As I've mentioned, this system is probably the most time-consuming football system I use, and you'll soon see why.

Here are the steps required by the system to calculate the odds on a particular game. We'll list the steps and then go back and give some examples:

- The first step of the system is to list all of the opponents the road team has played and the number of average points scored and allowed per game by each team.
- The second step is to add the opposition's average points for and points allowed and divide by the number of games played. This step will give an average number of points scored and an average number of points allowed by the road team's opposition.
- The third step is to divide the road team's points scored by the average points allowed by the road team's opposition.
- The fourth step is to divide the road team's points allowed by the average points scored by the road team's opposition.Let's use the Atlanta Falcons at the Detroit Lions as an example. Through six games, the Falcons have scored 104 points and allowed 148 points, which translates to 17.33 points for and 24.67 points allowed per game. The first step of the system calls for us to list all of the Falcons' opponents and their per-game averages, so we would have something similar to:

Minnesota 22.33-20.5

Houston 18.5-20.33

New Orleans 23-17.83

Tampa Bay 18.83-17

Dallas 26-18.16

Oakland 16.33-19.17

The second step calls for us to add up all of the totals and divide by the number of games played, which in this case is six. So, adding up all of the points scored by the opposition gives us 125.17 points (22.33+18.5+23+18.83+26+16.33=125.17). Diving 125.17 by six gives us 20.86, which is the average points scored by the teams the Falcons have played this season.

The second step also calls for us to do the same thing for the points allowed by Atlanta's opposition. Adding the totals up gives a sum of 110.83 points (20.5+20.33+17.83+17+18.16+19.17=110.83). Dividing by six gives a total of 18.47, which is the average number of points Atlanta's opposition has allowed during the season.

The third step is to divide Atlanta's average points scored (17.33) by the average number of points allowed by opponents, which is 18.47. Dividing 17.33 by 18.47 gives us a figure of .94. What this means, essentially, is that Atlanta is performing at 94-percent of an average offense, based on the opposition they have faced.

The fourth step calls for dividing the number of points the Falcons have allowed by the number of points the opposition has scored. In this case, divide 24.67 by 20.86 and you get a total of 1.18. In this case, Atlanta's defense is performing 18-percent**worse**than an average defense, based on the opposition they have faced. A total of 1.00 would be average, while a total under 1.00 would indicate the team is allowing fewer points than an average team. Therefore, a defensive total above 1.00 indicates the team allows more than the average number of points.

We will now do the same process for the home team, the Detroit Lions, who have scored 22.33 points per game and allowed 19.50 points per game for the purpose of our example.

The fifth step of the system calls for us to list all of the Lions' opponents, so we would have something similar to:

Green Bay 22.67-18.67

Minnesota 22.33-20.5

Chicago 20.5-22.17

Tampa Bay 18.83-17

Washington 16.5-13.67

Buffalo 22.17-17.33

The sixth step calls for us to add up all of the totals and divide by the number of games played, which in this case is six. So, adding up all of the average points scored by the opposition gives us 123 points (22.67+22.33+20.5+18.83+16.5+22.17=123). Diving 123 by six gives us 20.5, which is the average points scored by the teams the Lions have played this season.

The sixth step also calls for us to do the same thing for the points allowed by Detroit's opposition. Adding the totals up gives a sum of 109.34 points (18.67+20.5+22.17+17+13.67+17.33=109.34). Dividing by six gives a total of 18.22, which is the average number of points Detroit's opposition has allowed during the season.

The seventh step is to divide Detroit's average points scored (22.33) by the average number of points allowed by opponents, which is 18.22. Dividing 22.33 by 18.22 gives us a figure of 1.23. What this means is that Detroit is performing at 123-percent of an average offense, based on the opposition they have faced.

The eighth step calls for dividing the number of points the Lions have allowed by the number of points the opposition has scored. In this case, divide 19.5 by 20.5 and you get a total of .95. In this case, Detroit's defense is performing 5-percent **better** than an average defense, based on the opposition they have faced. A total of 1.00 would be average, while a total under 1.00 would indicate the team is allowing fewer points than an average team. Therefore, a defensive total above 1.00 indicates the team allows more than the average number of points.

### Performing the Actual Game Predictions

By now, the majority of the time-consuming work is done, but we still have more work to do. This section will show how the actual game predictions are calculated.

- The ninth step of the system is to add the road team's offensive percentage to the home team's defensive percentage and divide by two.
- The 10th step of the system is to add the home team's offensive percentage to the road team's defensive percentage and divide by two.

For the ninth step, we take Atlanta's offensive percentage (.94) and add Detroit's defensive percentage (.95) and come up with 1.89. Dividing this figure by two gives us a new figure of .945. This is Atlanta's performance figure.

The 10th step calls for us to take Detroit's offensive percentage (1.23) and add Atlanta's defensive percentage (1.18) to get a total of 2.41. Dividing this figure by two gives us a total of 1.21. This is Detroit's performance figure.

- The 11th step calls for us to add the road team's points scored to the home team's points allowed and divide by two.
- The 12th step calls for us to add the home team's points scored to the road team's points allowed and divide by two.

To perform the 11th step, we take Atlanta's average points scored (17.33) and add the average number of points Detroit has allowed, which is 19.5 to get a total of 36.83. Dividing by two gives us a total of 18.42. This is Atlanta's base offensive number.

The 12th step calls for us to take Detroit's points scored (22.33) and add Atlanta's points allowed (24.67), giving us a total of 47. Diving by two gives a total of 23.5. This is Detroit's base offensive number.

- The 13th step is to multiply the road team's base offensive number by its performance figure and subtract 1.5 points. The reduction in points is for playing on the road.
- The 14th step is to multiply the home team's base offensive number by its performance figure and add 1.5 points. Naturally, the addition in points is for playing at home.

For the 13th step, we take Atlanta's base offensive number (18.42) and multiply by Atlanta's performance figure (.945) and we get a new total of 17.41. We then subtract 1.5 from 17.31 to get a total of 15.91. This is the number of predicted points Atlanta will score.

In the 14th step, we take Detroit's base offensive number (23.5) and multiply by Detroit's performance figure (1.21) and we get a total of 28.44. Adding 1.5 points will give us a new total of 29.44, which is the predicted number of points Detroit will score.

Therefore, our prediction in the game is Detroit 29.44, Atlanta 15.91. Our predicted line is Detroit by 13.53 points.

Look for at least a five-point differential between the point spread and the predicted line before making a wager. In this case, you would wager on the Lions if they were favored by 8.5 or fewer points, while the Falcons would be a play if Detroit was favored by 19 or more points.

The system may seem a bit overwhelming at first, but once you have done it several times, it quickly becomes pretty simple.

For a number of years, the stats from the previous season were used for the first four weeks of a new season, but the changes in free agency have made that practice somewhat ineffective. For this reason, the system should perform best during the middle to the end of the season.

While the system is a bit time-consuming, it is a good indication of how teams are performing offensively and defensively throughout the course of the season.