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Expected Value Calculator

Calculate if a bet is +EV, the edge percentage, and optimal Kelly criterion bet size.

Start with a sample spot

Load a common scenario, then adjust the probability or price until it matches your view.

Your model's estimated true probability

The decimal odds from the market

Amount you plan to bet

Total bankroll for Kelly sizing

Results

Expected Value

+$10.00

Edge

+5.0 pts

Kelly Bet Size

$1,000

Implied Prob

50.0%

This is a +EV bet with a 5.0-point edge versus the listed price. Kelly suggests risking $1,000 (10.0% of bankroll). Quarter Kelly: $250.

How expected value is calculated

Expected Value measures the average profit or loss per bet over time:

EV = (Probability × Profit) - ((1 - Probability) × Stake)

Edge is the percentage advantage over the market:

Edge (points) = Your Probability - Implied Probability

Kelly Criterion determines optimal bet sizing:

Kelly % = (b × p - q) / b
where b = odds - 1, p = probability, q = 1 - p

Most professional bettors use quarter Kelly (25% of the Kelly suggestion) to reduce variance while maintaining positive growth.

This calculator compares your estimate to the listed decimal odds directly. For sportsbook markets, that implied probability may still include vig, so the displayed edge is against the quoted price, not a fully devigged fair line.

What is expected value? | What is Kelly criterion? | What is implied probability?

Frequently asked questions

Everything you need to know about expected value.

What is expected value in betting?
Expected value (EV) is the average profit or loss you can expect per bet over the long run. A positive EV (+EV) means the bet is profitable over time. It's the foundation of all quantitative betting and prediction market strategies.
How do I calculate if a bet is +EV?
Compare your estimated true probability to the market's implied probability. If your estimate is higher, the bet is +EV. For example, if market odds imply 40% probability but your model estimates 52%, you have a 12-point edge versus the quoted market price.
What is the Kelly criterion?
The Kelly criterion is a bankroll-sizing formula based on your edge and the payout odds. Full Kelly targets maximum long-run logarithmic growth, but it is volatile, so many professionals use quarter Kelly (25%) or half Kelly (50%) instead of staking the full amount.

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