Buying Half Points in Football
A statement repeated on betting forums often is "if buying half-points were +EV the bookmaker wouldn't sell them". This is just another football betting myth. In this article I'll discuss buying half-points for NFL football betting in great depth, touch on college football, and teach you easy to follow football betting strategy for buying half-points.
Buying Half Points Explained
Most online betting sites (Bovada being the exception) allow bettors to purchase half-points from a point spread starting at 10-cents each. So for example, if the point spread is -6.5 -110 you can purchase a half-point bringing it to -6.0 -120, or 2 half-points bringing it to -5.5 -130. If the point spread is +4.5 -105 you can purchase to +5.0 -115 or +5.5 -125. Now there are some exceptions to this.
- +3/-3 Always Cost More: For good reason 3 points is the most common margin of victory in football, purchasing across it either costs more or is restricted. Generally speaking it costs 25 cents for buying on or off the 3. So +2.5 to +3.0, +3.0 to +3.5, -3.5 to -3.0 and -3.0 to -2.5, those four half point moves cost 25 cents per half point. At some sites this is true only for NFL football, and not college football. For example, BetOnline charges only 15 cents for those four mentioned buys when the league is college football.
- +7/-7 Generally Costs More: The majority of online betting sites now charge 15 cents for buying on or off the 7; specifically, +6.5 to +7.0, +7.0 to +7.5, -7.5 to -7.0 and -7.0 to -6.5. A few sites charge more, for example Pinnacle Sports most often charges 17 cents for half-point buys involving the 7. It should be noted this is a rather new premium. I've found many local bookies in the US still sell these for 10 cents each, but online 15 cents or greater is standard.
The Value of Half Points
Finding the fair value of a half-point purchase requires two things 1) a push chart and 2) trivial mathematics. The table to the left is a push chart I created for NFL football; I'll discuss push charts briefly later in this article. As far as the math goes we'll need to first calculate our implied probability using the formula risk/return=implied probability, where return is stake+win. For example: -110 is risk $110 to win $100; the return is $210 ($110 stake + $100 win). So for -110 the implied probability is 110/210=0.5238 or in other words 52.38%. This tells us at odds -110 we need to win 52.38% of the time to break even.
Calculating the value of a half-point buy is now a matter of simple mathematics, so long as we already have a push chart. Considering we have one, let's a take a look at the value of moving a point spread from +6.5 -110 to +7.0. On the NFL push chart I just provided you'll see the favorite wins by 7 points 5.7% of the time. Now considering at +6.5 we lose on a -7 outcome, and now we push at -7 we're going to take half the 5.7% probability and add it to the 52.38% implied probability of -110.
Why only half? If we were moving from +6.5 to +7.5 we would take the full 5.7% value. However moving +6.5 to +7.0 we can only take half because on that number we push not win. Our opponent (the bookmaker) who has -7.0 also pushes. So half the 5.7% is in his -7.0 line, and half the 5.7% is in our line of +7.0. The same would be true moving +7.0 to +7.5; we take half the push probability of 7, because we're going from a push on 7 to a win on 7. Our increase is half the probability. When dealing with half points we're always either moving off a push (and therefore take half the probability of the number we move off of) or onto a push (and therefore take half the probability of the number we move on to).
So in this case of +6.5 to +7.0, half of 5.7% is 2.85%. We add this 2.85% to the +6.5 -110 implied probability 52.38% to get a new +7.0 implied probability of 55.23%. If you go to our odds converter and plug 55.23% into the implied probability field you'll see in American odds this is -123. This tells us moving +6.5 -110 to +7.0 is worth 13 cents. It also tells us that +6.5 -110 and +7.0 -123 have the same expected value.
An Important Lesson
When moving -110 to -123 the line moved 13 cents. I want to make it clear that cents are a meaningless evaluation figure. To best illustrate why, please allow me to exaggerate the point. We just showed that increasing a 52.38% probability 2.85% moves the American line 13 cents. Let's say however the line was +6.5 -280, which is risk $280 to win $100. Using Risk $280 / Return $380 = Implied Probability we see the implied probability of -280 is 73.68%. If we add 2.85% to this we get a new implied probability of 76.53. Go to our odds converter, plug in 76.53%, and you see this is American odds -326. So the same 2.85% increase in this case moved -280 to -326, and therefore was worth 46 cents, not 13 cents.
The lesson I'm attempting to give is the value of half points are progressive. If the line starts at -105 the value of a half point is less than if it started at -110; if the line starts at -115, then it's worth more. Likewise, when making multiple-half point purchases each half point purchased has greater value than the last. If betting sites didn't limit the number of half point we could buy at 10 cents each, we could purchase a ton of them to the point all bets we make are +EV. I'll come back to +EV half-point buys in a bit, but first let me cover the best betting sites for purchasing half points.
Best Betting Sites for Half Point Purchases
For the most part any betting website selling half-points at 25-cents for point spreads involving +3/-3, 15-cents for point spreads involving +7/-7 and 10 cents for all other point spreads is ideal. However, there are small little intricacies that make some sites more ideal than others.
BetOnline.com - While many online betting sites only allow bettors to purchase two or three half points at 10-cents each, BetOnline actually allows punters to purchase four. Remember the lesson earlier, because the value of half points is progressive each one you purchase is worth more than the last. So the fact that they sell four for 10 cents can be a huge plus. They also only charge 15-cents (instead of 25 cents) on college football point spreads involving +3/-3, and also don't charge a premium on the +7/-7 for college football either, offering 10 cents instead of the 15 cents many other sites charge.
JustBet.com - Although not as ideal as BetOnline, JustBet is decent for half point purchases. Here you can purchase 3-half-points maximum at 10 cents each, and they charge just 20 cents for the three on college football.
TopBet.com - Topbet ranks #1 on our list of sports betting bonuses, but when it comes to half point buys here you'll want to stick to only purchasing a maximum of 2 half-points or buying 5 or 6. This is because at TopBet the first two cost 10 cents each and the remainder cost 15 cents each. This makes buying 3 or 4 poor value, but buying 5 or 6 will often offset the loss in value.
5Dimes.com - 5Dimes is the nuts when it comes to half point buys. This is because they price half points unique depending on which point spread you're crossing. They also allow bettors to purchase them unmatched in the industry 10-20 half-points per game. They are a reduced juice sportsbook, and you'll quite often find the best value here.
I should note that while we love them for their great odds on football teasers, Bovada.lv isn't a good site for buying half points. This is because very rarely do they even offer the option, and when they do it's only on low value numbers such as buying +8.5 in NFL to +9. If you use them for other reasons, just avoid their half point buys.
Buying Half Point Strategy
I've already covered how buying half-point works and how to calculate their value, but I haven't discussed push charts. It's worth noting that season to season NFL push charts don't change very much and mine was last calculated going into the 2012/13 season, so it should be good for at least a few years. When dealing with college football you have two options #1 create a push chart, or #2 remove vig from Pinnacle Sports.
Push Chart Option - For this you're going to need a massive amount of historical data. One option to obtain this is by purchasing access to ATSdatabase.com for $49.00 for one month or $99.00 for a year. I personally don't find their service worth much and some of their data needs cleansing so paying $49.00 for one-month, followed by ripping all the data and putting it into your own excel spread sheets is probably best. From here what you'll need to do is find all similar games (paying attention to their over/under betting total as well as point spread), and then see how often they won by the related numbers. So, you might make push charts for totals under 44, totals 44.5 to 55.5, and totals over 56. From here you can take all points spreads +1.5 to -1.5 of the number you're looking to calculate for, and see how often they won by that number.
Removing Vig Option - This is a far better option. If you're from the US just register a fake account at pinnaclesports.com, because they don't accept US bettors; having an account gives you access to their dynamic lines. At Pinnacle the option to both buy points and sell points is available, and Pinnacle is a very sharp reduced juice betting site. Here you can change the point spread to any increment and then use the remove vig calculator contained in the lower section of my article on handicapping the betting market. So for example, on a betting line of -7 we first calculate their no vig -7/+7 price. We then calculate their no vig price on +6.5 and -6.5, and then on +7.5/-7.5. Here we can note the changes of what they're willing to let us buy and sell points at to see how much chance they're giving the seven pushing.
Proof Buying Half Points Can be +EV
Let's take case of a point spread that's +9.5 -110. As already covered earlier in this article the implied probability of -110 is 52.38%. I also provided a push chart that showed -10/+10 pushes about 4.9% of the time. If we decided to purchase two half points bringing the line to +10.5, our implied probability is 52.38%+4.9%=57.28%. If we plug this new percentage into our odds converter we see in American odds format this is -134. If the bookmaker was charging the fair price for +9.5 to +10.5 he'd charge us -134, yet every betting site I know of sells half points moving from +9.5 to +10.5 which costs just -130. If we already thought +9.5 -110 was a neutral or better value bet, we'd be foolish not to purchase two-half points here because doing so lowers the bookmaker's advantage.
Now considering 14 also has a 4.9% probability we can now determine the following 4-half point buys are always must purchases.
1) When betting +9.5 -110 always buy to +10.5 -130
2) When betting -10.5 -110 always buy to -9.5 -130
3) When betting +13.5 -110 always buy to +14.5 -130
4) When betting -14.5 -110 always buy to -13.5 -130
Although these are the best half point buys there are others. Let's take the example of a point spread +6 -115. The implied probability of -115 is 53.49%. If we were to buy this to +7.5 we would take half the probability of 6 which is 3.4%/2=1.7% and the full probability of 7 which is 5.7%. So, 53.49%+1.7%+5.7%= 60.89%. Using our odds converter we can see that 60.89% is -155.6 in American odds format. At betting sites the move +6.0 to +6.5 would cost 10 cents where the next two cost 15 cents each, because they involve the seven. So, 110+10+15+15=150; the betting site is giving us -150 when we just calculate the fair price for the extra points should have been -155.6.
To conclude, let me mention there's still vig in the initial lines of all these examples. However, in these spots buying half points did lower the bookmaker advantage. If the lines was already a +EV bet we made it better. Perhaps if it was slightly -EV and we were on the fence we could make it +EV with the half point purchase. The reason these numbers work is because I'm dealing with common margins of victory and also purchasing multiple half points (which remember each one you purchase has a higher value than the last). You'll want to avoid low value numbers. When it comes to half-point buying, our target numbers of 7, 10, 14, 17, and 21. If we can use multiple half points to cross these numbers more times than not we're increasing the value of our wager.
This concludes my article on buying half-points in football. If you've read this article in full, understand it, and are interested in buying half points for value I suggest also reading the following articles:
Author: Jim Griffin
Updated: March 2015
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