What Is Expected Value (EV)? How to Calculate a Value Bet
Many people bet by only looking at "who will win," but those who truly understand the board look at "whether this price is worth it." The tool for judging that is expected value (EV). It determines whether you profit or lose over the long run.
In short: EV = win probability × decimal odds − 1. A positive EV means the price is in your favour over the long run — that's a value bet.
The Expected Value Formula
Calculating expected value is actually very simple:
EV = Win Probability × Odds − 1
Understand It With an Example
Suppose the model gives a team a 55% chance to win, and the bookmaker offers decimal odds of 2.00.
EV = 0.55 × 2.00 − 1 = 0.10, i.e. +10%.
A positive expected value means: at this price, betting repeatedly over the long run earns an average of 0.1 per 1 staked. A line where the model's win probability exceeds the odds-implied probability is what's called a value bet.
The Probability Implied by the Odds
Take the reciprocal of decimal odds to get the market's implied probability. Odds of 2.00 → 1 ÷ 2.00 = 50%.
When your model's estimated probability (55%) is higher than the market's implied probability (50%), the EV is positive — meaning the market has "underrated" this outcome, and the value lies in that gap.
Why EV Matters More Than "Who Will Win"
A line with a 90% chance to win but odds of only 1.05 has an EV of 0.90 × 1.05 − 1 = −5.5% (negative — a long-run loser); whereas an underdog with just a 35% chance but odds of 3.5 has an EV of +22.5%.
So value isn't about "high probability" — it's about "whether the odds are mispriced." That's exactly what Sporta.AI does: it uses models to compute the win probability of every line in each match, then compares them against market odds to find positive-EV value bets for you.
FAQ
Does a positive expected value guarantee a profit?
Not necessarily. Positive EV means the average result is positive over many repeated bets in the long run, but a single match can still lose. It's a statistical edge, not a per-match guarantee.
How much EV makes a bet worthwhile?
There's no absolute standard, but in practice genuine value usually comes as a modest positive EV (e.g. +3% to +15%). An absurdly high EV (e.g. +50%) is often the model being overconfident or noise on a long-shot line — be careful.