Half Point Calculator
A half point calculator shows the fair odds and true probability of moving a spread or total by 0.5 points. Enter the game line and odds, and the calculator estimates what each alternate line should be worth.
How the Half Point Calculator Works
How alternate lines work
An alternate line is just a different version of the main market line.
If the main spread for a team is -4.5, an alternate spread might be -5.5, -5, -3.5, -3, and so on. The same idea applies to totals. If the main total is 221.5, alternate totals might be 219.5, 217.5, 223.5, or 225.5.
As the lines change, so to the odds. When the line gets easier (i.e., more likely to win), the price should become more expensive. For example, a main line of -3.5 at -110 with an alternative line of -2.5 might have odds of -120. When the line gets harder (i.e., less likely to win), the payout should increase. For example, a main line of Over 225.5 at -115 with an alternative line of Over 226.5 might have odds of -105.
The hard part is figuring out how much the price should move. That's where a half point calculator comes in.
How the half point calculator works
This calculator starts with the current market line and the market price, removes the vig, and then uses a model to give each alternative line a win probability. For NBA and college basketball, the calculator uses a distribution based on historical scoring patterns in those sports, and uses the market line as the center of the distribution.
There are a few different ways to calculate alternative lines and the value of a half point. Because basketball has close to Normal scoring distributions, using a Normal distribution is the easiest way. To learn more about other methods that work when a simple distribution doesn't work as well, read the Secrets of Sports Betting book and the Sports Betting for Serious Bettors course & Sports Betting for Aspiring Modelers course.
Why a half point isn't always worth the same amount
A lot of bettors talk about “buying a half point” as if every half point has the same value, when it reality it doesn't.
A move from -2.5 to -2.0 isn't necessarily worth the same as a move from -6.5 to -6.0. The value depends on where the starting point is (the market line) and how scoring distributions work in that particular sport.
Why spreads and totals affect each other
Spreads and totals are connected. High-scoring games tend to have more variance, meaning the range of possible outcomes is wider. That means the value of moving a spread can change depending on the total, and vice versa.
Why alternate line math differs by sport
Alternate lines can't be priced the same for every sport.
Basketball gives us a lot of recent scoring data and relatively stable distributions, so they're easier to model accurately. Other sports are different. NFL and college football have stronger key-number effects, especially around 3, 6, and 7 for point spreads. NHL and MLB are lower scoring and have different scoring distributions as well. The concept that the price changes as you move away from the main line is the same, but it will change very differently from sport to sport.
What this calculator tells you
The half point calculator tells you how much the price should change for different alternative lines. This matters a lot because sportsbooks tend to add even more vig to alternative lines than to the main line. They do this because they know the models aren't perfect, so they give themselves some room for error. They also have to figure out how to change the alternative lines in real time as the main spreads and totals change. The calculator can help you decide if the main line or alternative line is the better price.
Note that all models (including the sportsbooks' alternative line models) are based on averages and assumptions. If a particular game, player, team, or market is going to have a much different variance than average, the usual alternative line pricing may not apply. That opens the door to mispricing and +EV opportunities.
Half Point Calculator FAQ
What's a Half Point Calculator?
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A Half Point Calculator is a tool that determines the fair odds and probability when moving a spread or total by 0.5 points. It can be used to price alternate lines more accurately. To use it, enter the game line and odds, and the calculator shows what each alternate line is worth.
How do you calculate the value of a half point?
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You calculate half point value by comparing the win probability of the main line to the win probability of the alternate line. The difference between those probabilities gives you how much that half point is worth. A half point will be more valuable when it crosses an outcome that occurs more often, like 3-point spreads in NFL games. That's why half point values can change in different sports and markets.
How do alternate lines work in sports betting?
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Alternate lines are spreads or totals that have been moved away from the primary market line. If you move the line in your favor (e.g., moving from -7 to -6), the payout gets worse because your bet becomes easier to win. If you move the line against yourself (e.g., moving from over 223 to over 223.5), the payout improves because your bet becomes harder to win. Moving further away from the primary line results in larger price changes. Our Half Point Calculator helps you decide if the alternate line price is fair.
Does a half point matter more in some sports or leagues?
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Yes. A half point has different values depending on how scoring margins work in that sport. For example, hockey and soccer scores are based on 1-point goals, while American football scores increment by 1, 2, 3, or 6 points. Different leagues within the same sport can also have different scoring patterns. College football, for example, tends to have much higher scoring variance than the NFL does. These factors can dramatically change how much each half point is worth.
Do totals affect half point value?
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Yes. The total in the game changes the scoring variance, which in turn affects alternative line prices. In games that are lower scoring (e.g., soccer), a 0.5-point move can matter a lot; there's a big difference between a total of 2.5 and 3. In higher-scoring environments (e.g., basketball), a 0.5-point move won't be worth as much.
Is buying a half point worth it?
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It depends. Buying a half point only makes sense when the price you pay is better than the no vig fair value of the alternative line price.
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Positive EV example: The no vig fair odds of an alternative line of -7 are -110, and the sportsbook is pricing that alternative line at -108. Since the no vig fair odds imply a higher probability than the posted line, a bet on -7 at -110 is +EV.
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Negative EV example: The no vig fair odds of an alternative line of -7 are -110, and the sportsbook is pricing that alternative line at -112. Since the no vig fair odds imply a lower probability than the posted line, a bet on -7 at -110 is -EV.
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How accurate is Bettor Ed's Half Point Calculator?
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It's accurate within the assumptions of the model it uses. The calculator assumes the no vig fair odds are truly "fair", but if any information hasn't been factored in to those odds, then the results won't be accurate. It's best to use the calculator as a benchmark in markets where you can estimate no vig fair odds accurately.
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