How the point spread calculator works
A point spread is a handicap chosen so that both sides are close to even money. This calculator turns a spread into a rough win probability for the favourite and the underdog, so a spread can be compared with a moneyline price on the same game.
- Start from 50% at a spread of zero.
- Add an approximate amount per point of spread, tapering as the spread grows, to get the favourite's win probability.
- The underdog's probability is the remainder; both convert to fair moneyline odds as 1 divided by the probability.
Worked example
A favourite at −6.5.
- Roughly a 70% chance of winning outright, fair odds about 1.43.
- The underdog at +6.5 is roughly 30%, fair odds about 3.33.
This is an approximation calibrated to NFL scoring, not a market model. Use it to sanity-check a moneyline against a spread, not to price one.
Questions
- How accurate is the conversion?
- Approximate. The true relationship depends on the sport's scoring distribution and key numbers; the calculator uses a simple curve for American football and will be less accurate elsewhere.
- Why does the favourite's probability flatten at large spreads?
- Because beyond a certain margin the extra points change the outright win chance very little; the favourite already wins almost every game.
- Can I compare the result with a bookmaker's moneyline?
- Yes, that is its purpose. If the moneyline pays more than the fair odds implied by the spread, the two markets disagree and one of them is mispriced.
