Test whether a price is worth taking before you stake. This calculator compares your probability estimate to the market and shows the expected value per bet.
Spot value by comparing your edge to the odds.
Estimate expected profit or loss per stake.
Sanity-check bets before you commit bankroll.
Tools are informational only, not betting advice, and do not guarantee profit.
Check whether a price is value by comparing your probability to the market.
Find +EV bets
This calculator is an educational tool for understanding expected value in probability and exchange trading. It does not provide betting advice, tips, or predictions.
Expected value (EV) tells you whether a price is in your favour over the long run. If your estimated
win chance is higher than the market’s implied probability, the bet is theoretically value. Use this
calculator to sanity-check your edge before staking real money.
Worked example: Odds 3.2, stake £5, win chance 40%.
Win profit = £5 × (3.2 − 1) = £11.00.
EV = 0.40 × £11.00 − 0.60 × £5.00 = £1.40 per bet.
Always gamble responsibly. This calculator is for information only and does not guarantee profit.
What does positive EV mean?
It means your estimated probability is higher than the market’s implied chance, giving a theoretical edge.
Should I include commission?
If you are betting on an exchange, enter your commission rate to see a more realistic net EV.
Can EV be negative even if the odds look high?
Yes. If your estimated chance is lower than the market’s implied probability, EV will be negative.
When to use an expected value calculator
Expected value (EV) is the single most important concept in quantitative trading. It tells you the average profit or loss you can expect per bet if you were to repeat the same wager thousands of times. A positive EV means the odds are in your favour over time; a negative EV means they are not, regardless of any individual result.
Use this calculator before placing any trade where you have an estimate of the true probability. For instance, if you believe a tennis player has a 55% chance of winning but the exchange offers odds of 2.2 (implying only 45.5%), the calculator will show you the expected profit per pound staked and help you decide whether the edge is large enough to justify the trade.
Detailed worked example
You estimate that a football team has a 38% chance of winning. The exchange back price is 3.2 and you plan to stake £25.
Implied probability at 3.2: 1 / 3.2 = 31.25%
Your estimated edge: 38% − 31.25% = 6.75 percentage points
EV formula: EV = [p × (odds − 1) − (1 − p)] × stake
This tells you that, on average, this bet returns £5.40 profit per occurrence. Over 100 identical bets, you would expect roughly £540 in profit, though individual results will vary due to variance. The key insight is that a single losing result does not make the bet wrong — what matters is whether the EV was positive at the time you placed it.
Common mistakes with expected value
Overestimating your edge: EV calculations are only as good as your probability estimates. If your 38% estimate is actually 32%, the bet becomes negative EV. Be honest about your analytical accuracy.
Ignoring commission: Exchange commission reduces your actual return on winning bets. A marginally positive EV can become negative after a 2-5% commission is applied.
Judging by short-term results: A positive EV bet can lose ten times in a row and still be the correct decision. EV is a long-run concept — it requires volume to manifest.
Forgetting about opportunity cost: Tying up your bankroll in a marginally positive EV bet means you cannot use those funds for a higher-EV opportunity elsewhere.
