Expected Value (EV) in Sports Betting

Expected value (EV) in sports betting

Expected value (EV) is the average profit (or loss) you’d expect per bet if you could repeat the same wager many times. EV is not a guarantee for one game. It’s a long-run concept.

The EV formula (single bet)

For a single bet:

• EV = p(win) × profit − (1 − p(win)) × stake
• p(win) is your estimated true probability (0–1)
• profit is what you win (excluding your stake being returned)

Worked example (-110)

Assume:

• Odds: -110
• Stake: $100
• Your estimated win probability: 55%

At -110, a $100 stake returns about $90.91 profit when you win. EV becomes:

• EV = 0.55 × 90.91 − 0.45 × 100
• EV ≈ 50.00 − 45.00 = +$5.00

Interpretation: if your 55% estimate is correct, you’re making about $5 per $100 in the long run.

Break-even win rate

Every price has a break-even probability. That’s simply the implied probability from the odds. For -110 the break-even rate is about 52.38%. If your estimate is above that, EV turns positive (all else equal).

EV vs ROI

• EV ($): dollar expectation for the stake you enter.
• ROI (%): EV divided by stake (edge quality). ROI doesn’t change when you change stake; EV dollars do.

Common mistakes

• Guessing win %: EV becomes a fantasy number if the probability is just vibes.
• Ignoring vig: odds reflect the book’s margin; implied probability is break-even, not “true.”
• Small sample thinking: positive EV can lose for weeks. That’s variance, not “proof” it doesn’t work.

How to use BettorCalc correctly

1. Convert odds to break-even (implied probability).
2. Only enter a win % when you have a reason (model, matchup, market comparison).
3. Use EV/ROI to compare bets, not to “guarantee” wins.