Expected value is the single most important concept in profitable sports betting. It’s the mathematical answer to “is this bet worth placing?” Every professional bettor, every sharp, every quantitative model comes back to the same thing: EV.
What is Expected Value?
Expected value (EV) is the average amount you’d win or lose per bet if you placed the same bet an infinite number of times. It accounts for both the probability of winning and the payout.
+EV (positive): The bet is expected to profit over time
-EV (negative): The bet is expected to lose over time
0 EV (neutral): Break-even
A slot machine is -EV. The house always has an edge. +EV betting flips that dynamic — you become the house.
The EV Formula
EV = (Win Probability x Profit if Win) - (Loss Probability x Loss if Lose)
Example
A bet at +200 odds with a true win probability of 40%:
Profit if win: $200 (on a $100 bet)
Loss if lose: $100
Win probability: 40% (0.40)
Loss probability: 60% (0.60)
EV = (0.40 x $200) - (0.60 x $100) = $80 - $60 = +$20
Every time you place this $100 bet, you expect to profit $20 on average. That’s a strong +EV play.
Another Example
A bet at -110 odds with a true win probability of 50%:
Profit if win: $90.91
Loss if lose: $100
Win probability: 50% (0.50)
EV = (0.50 x $90.91) - (0.50 x $100) = $45.45 - $50 = -$4.55
This is a -EV bet. The standard -110/-110 line at 50/50 probability always loses money due to the vig. You need a 52.4% win rate to break even at -110.
Try the expected-value-calculator→
How to Find True Win Probability
The EV formula is simple. The hard part is estimating the true win probability. There are several approaches:
No-Vig Fair Odds
Strip the vig from sharp sportsbook lines to estimate the market’s true probability. If Pinnacle (a sharp book) prices a team at 55% after de-vigging, that’s a solid estimate of fair value.
Model-Based
Build or use statistical models that project outcomes based on data. Advanced models combine multiple data sources — historical performance, matchups, pace, weather — to estimate probabilities.
Market Consensus
Compare odds across 10+ sportsbooks. The average implied probability, after removing vig, gives you the market consensus. When one book deviates significantly from consensus, that’s where value lives.
EV vs. Win Rate
High EV doesn’t mean a high win rate. You can be extremely profitable at a 40% win rate if you’re consistently betting underdogs at +200 when the true probability is 40%.
| Odds | True Win % | Win Rate Needed to Break Even | EV per $100 at True % |
|---|---|---|---|
| -110 | 52.4% | 52.4% | $0 |
| +100 | 55% | 50.0% | +$10 |
| +150 | 45% | 40.0% | +$12.50 |
| +200 | 40% | 33.3% | +$20 |
| +300 | 30% | 25.0% | +$20 |
Notice that +200 at 40% and +300 at 30% have the same EV per bet. Value comes from the gap between true probability and implied probability, not from the odds alone.
Variance and Sample Size
+EV bets lose all the time. That’s variance. You can place a +EV bet and lose it — that doesn’t mean the bet was wrong.
Think of it like poker. Going all-in with pocket aces is +EV. You’ll still lose about 20% of the time. But you’d make that play every single time because the math is on your side.
The law of large numbers means that over hundreds and thousands of bets, your actual results converge toward the expected value. The more bets you place, the more your results reflect your edge.
Key Takeaways
EV tells you the average profit/loss per bet over the long run
A bet is +EV when your estimated win probability exceeds the break-even probability implied by the odds
You don’t need to win most of your bets to be profitable — you need to consistently find +EV spots
Variance means short-term results can look nothing like your long-term edge — trust the math and the sample size
