Commercial
Expected Value (EV)
Last reviewed 24 September 2026
What is EV?
The average result of a bet if it could be repeated indefinitely, calculated by weighting each outcome by its probability. Positive EV is the basis of profitable betting.
Key takeaways
- Expected value is the sum of each possible outcome multiplied by its probability: the average result of a bet repeated indefinitely.
- A 10 stake at 3.00 on an outcome with a true 40% chance has an EV of plus 2.00; at a 30% chance the same price is negative EV.
- Operators price every market to carry negative expectation for customers and model bonuses so their expected cost stays below player value.
Why it matters
Expected value is the single number that decides whether a bet is worth making. It is the sum of each possible outcome multiplied by its probability. A 10 stake at decimal odds of 3.00 on an outcome with a true 40% chance has an expected value of 0.40 times 20 profit minus 0.60 times 10 stake, giving plus 2.00: a positive-EV bet. Change the true chance to 30% and the same price becomes negative EV.
The concept matters because it separates process from result. A positive-EV bet can lose, and often will, while a negative-EV bet can win; only over a large sample does expectation dominate variance. Serious bettors therefore judge decisions by EV rather than by profit and loss, and use closing line value as a proxy because true probabilities are unobservable. For operators the same maths runs in reverse: every priced market is designed to carry negative expectation for the customer, and bonus terms are modelled so that the expected cost of the offer stays below the expected value of the player acquired.
Frequently asked questions
How is expected value calculated in betting?
Multiply each possible outcome by its probability and add the results. For a 10 stake at decimal odds of 3.00 on an outcome with a true 40% chance, the calculation is 0.40 times the 20 profit, minus 0.60 times the 10 stake, which gives plus 2.00, so the bet is positive EV. If the true chance were 30%, the same price would give minus 1.00, a negative-EV bet.
Can a positive expected value bet lose?
Yes, and often will. Expected value describes the average result over many repetitions, not the outcome of a single bet, so a positive-EV bet can lose and a negative-EV bet can win. Only over a large sample does expectation dominate variance. That is why serious bettors judge decisions by EV rather than short-run profit and loss, and use closing line value as a proxy because true probabilities cannot be observed.
Why does expected value matter for operators?
Operators run the same maths in reverse. Every priced market is designed to carry negative expected value for the customer, which is the source of the house edge and the bookmaker margin. Bonus terms are modelled on the same basis, so that the expected cost of an offer, after wagering requirements and likely play, stays below the expected value of the player it acquires.