A price is a probability in disguise. Once you can convert one into the other, every other idea in betting becomes arithmetic you can check.
A betting price is a probability wearing a disguise. Converting one into the other is the single most useful skill in betting, because it turns an opinion you cannot argue with ("the Chiefs are -250") into one you can ("the market says 71.4%, and I think it is closer to 65%").
The number you get is called the implied probability. Two formulas cover every American price.
If you prefer decimal odds there is only one formula, and it is easier: 1 ÷ decimal. A price of 2.50 implies 1 ÷ 2.50 = 40%. Same answer.
The price implies a 71.4% chance of winning.
Here is the thing that surprises everyone the first time. Take a normal game where both sides are priced at -110 and convert both:
One of those two things is certain to happen, so the real probabilities must add to exactly 100%. They add to 104.76% instead. The extra 4.76 percentage points are not a rounding error and not a mistake — they are the sportsbook's fee, built into both prices at once.
That excess has a name: the overround. Implied probability always overstates the real chance, on every side of every market, because the fee is inside it.
If you compare a price against its own implied probability, you will always find a small negative edge — you are comparing the price with itself plus the fee. Any honest value calculation has to remove the fee first. That is the next lesson.
Implied probability has a second reading. It is also the win rate you need to break even at that price.
| Price | Implied probability | You must win this often to break even |
|---|---|---|
| -200 | 66.67% | 66.7% |
| -150 | 60.00% | 60.0% |
| -110 | 52.38% | 52.4% |
| +100 | 50.00% | 50.0% |
| +150 | 40.00% | 40.0% |
| +300 | 25.00% | 25.0% |
The -110 row is the one worth memorising. 52.38%. Betting standard spreads, picking winners at 52% — which is genuinely better than a coin flip — still loses money slowly. That gap between 50% and 52.38% is the entire business model of a sportsbook, and it is what the next lesson is about.
Type any price and see its decimal, fractional and implied-probability forms at once. Use the odds converter.