How to Calculate EV in Sports Betting
Expected Value (EV) is the single most important concept in profitable sports betting. This guide walks through the formula, a step-by-step worked example, how to remove bookmaker vig, and how to size bets optimally using the Kelly Criterion.
1. The EV Formula
Expected Value measures the average amount you expect to profit (or lose) per unit staked, over a large number of identical bets. The general formula is:
For a decimal-odds bet with a stake of 1 unit, this simplifies to the EV percentage (edge):
Any bet with EV% > 0 is a value bet. The higher the EV%, the greater the edge per unit staked.
2. Step-by-Step Example
Let's calculate the EV for a real scenario: Spartak Moscow vs CSKA Moscow — Home Win.
3. Removing the Vig (No-Vig Probability)
Every bookmaker adds a margin (vig) so that their implied probabilities sum to more than 100%. To find the true probability, you must normalise them. For a two-outcome market:
For three-way markets (football 1X2), the same principle applies — divide each implied probability by the sum of all three. Pinnacle's margin is typically 2–3%, making it the best reference market for no-vig probability extraction.
4. Kelly Criterion — Optimal Bet Sizing
Knowing a bet has positive EV is only half the equation. Staking too much amplifies ruin risk; staking too little under-exploits the edge. The Kelly Criterion gives the mathematically optimal fraction of bankroll to stake:
Using our earlier example (EV% = 9.21%, Odds = 2.55):
Kelly% = (0.0921 / 1.55) × 100
Kelly% = 5.94%
Full Kelly can lead to aggressive swings. Most professionals use fractional Kelly (25–50% of the Kelly recommendation) to reduce variance. The EVBets calculator computes both full and fractional Kelly automatically.
FAQ
What is a good EV percentage for a value bet?
Most professional value bettors target EV% of 2% or higher. EVBets displays the EV% for every opportunity so you can filter by your preferred threshold.
What is the difference between EV and ROI in betting?
EV is the expected return per bet calculated before settlement, based on probabilities. ROI is the actual return on investment over historical settled bets. Over a large sample your ROI should converge to your average EV%.
Can I calculate EV without a sharp bookmaker reference?
Yes, but it requires a statistical model (Elo ratings, Poisson for football). Without an external benchmark it is difficult to validate your estimates — the sharp-market comparison method is more reliable for most bettors.