How the half point calculator works
Buying a half point moves a spread or total in your favour at a worse price. Whether it is worth it depends on how often the half point turns a push or a loss into a win, against how much the price got worse. This calculator puts both sides of that trade in the same units.
- Implied probability of the original price and of the new, worse price; the difference is what the half point costs you.
- The push probability is how often the game lands exactly on the number you are moving through: that is how often the half point changes your result.
- If the gain in win probability from the half point is bigger than the cost in implied price, buying it is worth it.
Worked example
From 1.91 to 1.80 to buy through a number that lands 3.5% of the time.
- Implied cost: 55.6% − 52.4% = 3.2 points of probability.
- Gain: turning a 3.5% push into a win is worth about 1.75 points, half the push chance, since a push returned the stake.
On these figures the half point costs more than it earns. Key numbers in NFL, 3 and 7, land far more often and can justify the price.
Questions
- Where do I get the push probability?
- From historical margin distributions for the sport: how often games land exactly on the number. It varies enormously by number, which is the whole point of key numbers.
- Is a half point through a key number always worth buying?
- Only when the price cost is less than the value of the landing frequency. Bookmakers charge more to buy through key numbers for exactly that reason.
- Does this apply to totals as well as spreads?
- Yes. The same comparison works for any line you can move for a price.
