Value Betting: What Is Expected Value and How to Calculate It
An explanation of expected value in sports betting: how to tell if an outcome is mispriced, and why maths matters more than short-term results.
What expected value means
Expected value (EV) is the mathematical expectation of profit per unit staked. A positive EV bet is profitable in the long run. A negative EV bet is a losing strategy, regardless of whether it wins today.
The formula: EV = (probability of winning × profit) − (probability of losing × stake). For example, if the true probability of an outcome is 55% but the bookmaker's odds imply 47.6% (odds of 2.10), then EV = 0.55 × 1.10 − 0.45 × 1 = +0.155 per unit. Every such bet returns +15.5% on average over time.
How to find mispriced outcomes
The core question: is your probability estimate more accurate than the bookmaker's? This requires either a quantitative model or the ability to spot situations where the market systematically errs — overrating popular teams, underrating statistically strong strategies, or reacting slowly to important news.
A simple check: compare the implied probability of the odds with independent market estimates. If several bookmakers price a market around 1.80, but one offers 2.10 on the same outcome, there's likely a pricing inefficiency.
Bookmaker margin and its effect on EV
Bookmakers build a margin into odds so that the sum of all implied probabilities exceeds 100%. On top-tier matches the typical margin is 3–6%; on lower-liquidity markets it can reach 15–20%.
This means to achieve positive EV, you need to estimate outcomes more accurately than the bookmaker's line already reflects. That's why value betting requires discipline and a large sample size — short-term results are heavily influenced by variance.
Variance and sample size
Even with a stable positive EV, you can lose 50–100 bets in a row. That's normal probability at odds of 2.0+. Panic and strategy changes in a downswing are the main reason players with the right approach still lose money.
For EV to materialise, you need a sample of several hundred bets minimum. That's why bankroll management and betting a fixed percentage of your stake are more important than finding the 'perfect' system.