Expected value needs two inputs: a probability and a price. The price is on the screen. The probability is hiding inside it. Get this one wrong and every EV calculation you ever do is wrong too.
One decimal place. No calculator shame — the point is the reading, not the arithmetic.
| What we're asking | Your answer |
|---|---|
| Detroit at 1.80 implies | |
| Boston at 2.05 implies | |
| The two added together | |
| The bookmaker's margin | |
| Detroit wins neededPER 100 BETS · TO BREAK EVEN |
Two to sit on before you check. Why doesn't the market total 100? And can both sides be positive EV at the same time?
The market doesn't total 100 because it isn't meant to. That extra 4.3% is the bookmaker's fee, charged on both sides at once. Back Detroit and you're paying it. Back Boston and you're paying it. Sit out and you're not — which is why sitting out is a real option, not a wasted night.
$100 on Detroit at 1.80, one hundred times, winning exactly 55.6 of them:
Eight dollars across ten grand. That's zero EV — the exact point where a bet stops being a bet and starts being a transaction.
Detroit needs 55.6 wins per 100. Boston needs 48.8. Add them: 104.4 wins out of 100 games. There aren't that many. Back both and you're guaranteed to lose the margin — which is exactly the design.
Next activity you'll meet the EV formula properly. It has two inputs and only two: your probability, and the odds. The number you just calculated isn't your probability — it's the market's, with the fee still attached. But it's the benchmark you measure yours against.
Most people look at 1.80 and think Detroit's favourite. What it says is: Detroit has to win 56 times in 100, and you're paying 4.3% for the privilege of finding out. Being right more often than you're wrong was never the bar. Clearing the margin is.