Key numbers in NFL line betting

What are the key numbers when betting NFL lines? What margins are more common than others? Are some half points worth more than others? Andrew takes a look at 20 seasons of NFL results to investigate.

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I had the chance to appear on the XTraders podcast again last week, this time to talk the in's and out's NFL betting. During the 3 hours myself and Matt spoke (no, we didn't record the whole 3 hours) we discussed many betting related topics. One of the points I raised was the topic of 'key numbers' in NFL line betting.

What are key numbers?

Key numbers in NFL line betting come from the fact that some margins of victory are far more common than others. How does this impact upon betting? Well it means that some between some betting lines and line movements are more significant than others.

In this piece we will dig into 20 seasons of NFL results and betting lines to investigate what exactly key numbers are and how they can impact upon your NFL betting.

The Key Numbers

Firstly we will start by looking at the frequency of winning margins in the NFL the last 20 seasons. In doing so, we will see which margins represent key betting numbers in the NFL.

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Here we can see that the most common winning margin in the last 20 seasons of NFL games, is 3 points. This margin occurred just over 16% of the time and was almost twice as common as the next most frequent margin, 7 points, which occurred almost 9% of the time the last 20 seasons. Combined, these two margins account for 25% of all margins the last 20 seasons, making these two margins the most significant of any key numbers in NFL betting.

The next most frequent margin was 10 points, occurring just over 6% of the time, with the margins 6 points and 4 points both occurring the next most frequently at just over 5%.

Obviously each of these common margins are most common due to NFL scoring, with a field goal being 3 points and a converted touchdown, 7 points, leaving margins like 11 or 8 for example, of little chance occurring.

When the line is set at 3 points

So let's take a look at the significance of key numbers in real betting situations. Firstly we will look at results when the line has been set at 3 points the last 20 seasons. Here we will be looking at the cover rates in these games when taking alternative line handicaps.

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Here we can see the obvious impact of crossing a key number. Over the last 20 seasons, when the line was set at -3, you would have covered the line just over 49% of the time. As you would expect, it's roughly a 50-50 success rate.

But when we look at the difference between taking a -2.5 point line against a -3.5 point line in these games, we see a serious difference in results. Had you taken a -2.5 line in a game where the line was set at 3 points the last 20 seasons, you would have covered the -2.5 line just over 54% of the time. Meanwhile, had you taken the -3.5 line in these games, you would have covered that line just over 44% of the time, a difference of 10%.

How significant is this?

Well, let's compare that 10% improvement across a single point adjustment from -2.5 to -3.5. Take a look at the difference between taking a straight up win line (-0.5 points) against a -2.5 line in these games. The difference in cover rates was around 4%. Thats just a 4% improvement for a 2 point line adjustment.

Let's look at another example. The difference in success rate between -2.5 and -3.5 of 10%, is the same for a full 3.5 point line adjustment from -3.5 to -7, where the success rate of covering the adjusted line goes from just over 44% to just under 34%.

The significance of crossing a key number should be clear. The difference between taking a -2.5 and a -3.5 is significant in comparison to other 1 point line differentials and crossing the key number of 3 is something you shouldn't do lightly. It might only seem like a point, but the impact upon your success rate is dramatic if you're not aware of the fair price for such a line adjustment. Likewise, taking an underdog +2.5 over a +3.5 might seem like your're only giving a point, but it's as significant as taking a team +3.5 over +7.

When the line is set at 7 points

Let's take a look then at the other key number. Here we will be looking at games where the line was set at -7 the last 20 seasons, and looking at the success rate of alternative lines in these games.

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We can see the significance of crossing this key number, with the cover rate of a -6.5 line in these games at just over 50%, while -7.5 succeeding just under 45% of the time. Here we are looking at around a 5% improvement for a single point adjustment.

This difference is roughly the same in this scenario as taking a -4.5 line to a -6.5 line, a 2 point line adjustment. It's also about the same as taking an adjusted line -8 to -11.5, a full 3.5 point adjustment for the same 5% improvement in cover success.

Further, we can also see a similar improvement in success rate across the key number of 3 points in these games, with the cover rate for -2.5 running at almost 68% in games with the line set at -7 the last 20 seasons, as opposed to the -3.5 line which has covered at over 57%. Again, like the analysis of games where the line was set at -3, the cover rate improves around 10% acorss the key number of 3.

So what did we learn?

The lesson should be clear - be careful when buying or selling points across the key numbers of 3 and 7. The difference between getting a half point to your advantage at the same price across these key numbers can make a significant difference to your long-term betting success. It might only seem like half a point, but consistently taking a -2.5 over a -3 at the same price, will serve you well over the duration of your time as a NFL bettor.

Look at it this way. Let's say you made 100 bets at -2.5 at odds of 1.90 the last 20 seasons, as opposed to the official -3 line at the same odds. Taking the -2.5 would have seen you claim around 2.7% profit for those 100 bets, while taking the -3 at the same price, would have seen you make a loss of around 6.5%. Again, the significance of getting a half point to your advantage around key numbers should be clear.

This highlights the importance of having a number of bookmakers to shop for lines at. If you're only betting lines at one bookmaker, you're not giving yourself the best chance of succeeding. Having a minimum of three bookmakers will give you greater opportunities to find the best line available and see you often finding a key half point right where and when you need them.

And lastly, be careful when buying points and taking alternative lines. Expect your bookmaker to ask a tough price to buy a point to your advantage across a key number, particularly the key number 3. But if they're asking you similar prices to buy points across 4, 5 or 6 point lines, they're only hoping to take advantage of the naive bettor who wants to buy up what are for the majority of the time, useless points.