Read the odds
Turn betting lines and prediction market prices into probabilities, and find the bookmaker's cut.
Example lines, not live prices. Type any American odds (like −150 or +130) to try your own.
| Side | Implied | Fair | Your EV / $100 |
|---|---|---|---|
| Team A | 52.38% | 50.00% | −$4.55 |
| Team B | 52.38% | 50.00% | −$4.55 |
The two add to
104.76%
Bookmaker's cut
4.55%
Real probabilities add to 100%. These add to 104.76%; the extra is the price of playing. A bet only has positive expected value when your chance is higher than the implied one.
What’s going on
American odds. A minus number is how much you risk to win $100; a plus number is how much you win on $100. The implied probability is |a| / (|a| + 100) for a favorite and 100 / (a + 100) for an underdog. So −150 means 60.0% and +150 means 40.0%.
Prediction markets are simpler: a contract that pays $1 if the event happens and trades at 63¢ implies a 63% chance.
Add both sides of a line and you get more than 100%. On a −110 / −110 line each side implies 52.38%, together 104.76%. That extra is the overround; the bookmaker’s margin is 1 − 1/1.0476 ≈ 4.55%. Divide each side by the total to get the fair, no-cut probabilities.
A bet has positive expected value only when your probability beats the implied one: EV = p × profit − (1 − p) × stake. At −110 you need to be right 52.38% of the time just to break even.
Example lines, not live prices. For learning, not betting advice.