Expected Value in Sports Betting, Explained
What expected value (EV) means in sports betting, how to calculate it from a fair probability and a price, and why small edges add up over many bets.
By DataOdds Team
2 min read
In short: Expected value is the average profit or loss a bet would return if you placed it many times. Multiply the win probability by the profit if it wins, subtract the loss probability times the stake, and a positive result means the price is better than fair.
Expected value, or EV, answers one question: if you could place this exact bet thousands of times, would you make or lose money on average? It is the single most useful number for judging a price.
The formula
EV = (P(win) × profit if win) − (P(loss) × stake)
P(win) should be your best estimate of the true chance of the outcome. Most bettors use the market's no-vig fair probability, because it strips out the book's margin.
A worked example
Say the fair probability of a side winning is 52%, and you are staking $100.
| Price | Profit if it wins | EV per $100 |
|---|---|---|
| -110 | $90.91 | -$0.73 |
| -105 | $95.24 | +$1.52 |
| +100 | $100.00 | +$4.00 |
The outcome is identical in every row. Only the price changes, and that alone decides whether the bet is worth making. This is why line shopping matters: the same view on a game can be a losing bet at one book and a winning bet at another.
Why small edges matter
A +1.52% edge sounds tiny, but EV scales with volume. Over 1,000 bets of $100 at that edge, the expected profit is about $1,520. Results will swing around that number, sometimes a lot, but the average is what you are aiming at.
Common mistakes
- Using the book's own implied probability. That number includes the vig, so every bet looks slightly negative.
- Judging a bet by its result. A winning bet at a bad price was still a bad bet.
- Trusting huge edges. A 15% edge in a major market is usually a stale line or a mistake, not free money.
Where to go next
Expected value depends on a good fair price. If you have not already, read the post on removing the vig to see how fair probabilities are calculated.
Frequently asked questions
- How do you calculate expected value for a bet?
- EV = (win probability × profit if it wins) − (loss probability × stake). Use a fair, no-vig probability for the win probability rather than the book's implied probability.
- Does a positive EV bet always win?
- No. Expected value describes the average result over many bets. Any single bet can lose, and a run of positive EV bets can still lose money over a short sample.
- What is a good EV percentage?
- Edges in liquid markets are usually small, often in the low single digits as a percentage of stake. Larger apparent edges are more often a stale or mistaken price, so check them carefully.
For educational purposes only. Bet responsibly and only where legal.
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