Half Point Calculator: What a Half Point Is Worth
A half point on a spread or total changes the chance to cover by the height of the result curve at the line, times 0.5 divided by the standard deviation. Near the middle of the curve it is worth about one to two percentage points, and more at key numbers in real data.
Key facts
- A normal (bell-curve) distribution is a common model for the difference between two teams' scores.
- The probability change from a small move equals the curve's height at the line times the size of the move.
- At the center of a standard bell curve the height is about 0.399 divided by the standard deviation.
Buying a half point costs money, and selling one gets you paid. Whether the price is right depends on how much probability a half point actually carries. This calculator uses a smooth model so you can see the size of the effect, and shows where it stops being accurate. It runs in your browser, sends nothing anywhere and forgets your numbers when you close the page.
Half point calculator
Turn on JavaScript to use the calculator. The worked example below shows the same math by hand.
What you enter and what you get
You enter
- Line (spread or total): For a favorite's spread use the number you'd lay, such as -3 as 3 with a projection of that sign.
- Your projected margin: Same scale as the line.
- Spread of results (standard deviation): An assumption you set. Check it against real results for your sport.
You get
- One half point is worth
- Chance to cover at 3
- At 3.5 (half point easier to beat)
- At 2.5 (half point harder)
- Price shift that equals a half point
How the calculator works
- Treat the game margin as a bell curve centered on your projection.
- Find how far the line sits from your projection, in standard deviations.
- The chance to cover is the area of the curve beyond the line.
- Move the line by half a point and compare. The difference is the value of the half point.
A worked example
A line of 3, a projection of exactly 3, and a standard deviation of 13 points.
| Item | Result |
|---|---|
| One half point is worth | 1.53 pts |
| Chance to cover at 3 | 50% |
| At 3.5 (half point easier to beat) | 48.5% |
| At 2.5 (half point harder) | 51.5% |
| Price shift that equals a half point | 1.53 pts of implied probability |
What the calculator leaves out
- Real margins cluster on certain numbers, so this smooth curve understates a half point at those numbers.
- The standard deviation is yours to set. The answer scales with it.
- It models one line, not how the price changes when you buy points.
How we checked it
Before it went on the page we checked it against the model's own definition: at the middle of the margin curve, the value of half a point has to equal the height of the curve there. The calculator is also run against thousands of odd entries such as blanks, zeros and huge numbers, so a bad entry shows a plain prompt and never a wrong number. The worked example above comes from the same code the calculator runs.
At a sweepstakes sportsbook
Sweepstakes sportsbooks don't all offer alternate lines, and buying points may work differently or not at all. Check what your site offers before pricing a half point. How we make our guides explains where our numbers come from.
Betting math is not betting advice. Only play with money you can afford to lose, and if gambling stops being fun, call or text 1-800-GAMBLER.
Frequently asked questions
Is a half point worth the same on every number?
No. In sports with common final margins, a half point across one of them is worth more than a half point elsewhere.
Where do I get the standard deviation?
From past results for the sport and league you care about. Different sports have very different spreads of margin.
Does this tell me whether to buy points?
It tells you how much probability a half point carries. You still compare that with the price you'd pay.
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- Probability, Wikipedia (read 2026-10-05)
- Sports betting, Wikipedia (read 2026-10-05)
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