Expected Value (EV) Calculator

Expected value, or EV, is what a bet is worth on average if you could make it over and over. Positive EV means the price is paying more than your estimate of the outcome says it should; negative EV means it is paying less.

It is the difference between a good bet and a winning bet, and the two are not the same. A +EV bet loses often — sometimes many times in a row. What makes it worth taking is that across enough repetitions the arithmetic pays, in the same way a casino profits from a house edge without winning every hand.

It depends entirely on your probability being better than the market’s. That is the hard part, and no calculator does it for you.

Expected value is the average result of a bet if you could place it over and over. It has two ingredients: what you win when you are right, weighted by how often that happens, minus what you lose when you are wrong, weighted by how often that happens. If the first term is bigger, the bet has positive EV and repeating it makes money. If not, it doesn’t, however good the pick feels.

The entire answer hinges on one input: your win probability. The odds are a fact you can read off a screen; the probability is an estimate you are responsible for. Feed in a number you like rather than one you can defend and the calculator will faithfully report a positive EV that does not exist. It has no way to check you — treat the output as a test of your estimate, not proof of it.

A useful discipline is to work backwards. The price implies a break-even rate; your estimate has to beat it, and by enough to survive being slightly wrong. Two points of edge on a genuine 55% read is a real advantage. Two points of edge on a number you guessed is noise. The fair-price line shows the shortest price you should accept, which is often more actionable than the EV figure itself.

Finally, EV is a long-run average and nothing else. A bet with +$4.55 of expected value never returns $4.55. It wins or it loses, and the average only appears across hundreds of similar bets — which is why staking size, not EV alone, decides whether you survive to see it.

A bet at +110 that you judge to be a 55% chance, staking $100. Decimal is 2.10, so a win profits $110 and a loss costs $100.

EV = (0.55 × $110) − (0.45 × $100) = $60.50 − $45.00 = +$15.50, or 15.5% of stake. The price implies 47.62%, so your edge is 55 − 47.62 = 7.38 points — large, and worth being sceptical about. Edges that size are rare and usually mean the estimate is wrong, not that the market is.

The fair price for a 55% chance is 1 / 0.55 = 1.818, about −122. So anything longer than −122 is a bet worth making on that read, and anything shorter is not — including −110, which looks like a bargain and is barely one.

Where do I get the win probability?

From your own model, your read on the matchup, or a sharper market’s no-vig price. It cannot come from the odds you are evaluating — that would make every bet exactly break-even by construction.

What counts as a good edge?

In liquid markets, one to three percentage points is a real, hard-won edge. Anything above five should make you re-check the estimate before the bet: large apparent edges usually mean stale information or a misread rule, not free money.

Does positive EV mean I will win this bet?

No. It means that if your probability is right, bets like this one make money on average across many repetitions. Any individual bet still wins or loses in full, and a positive-EV bet can lose many times in a row.

How do I turn EV into a stake size?

Use the Kelly criterion calculator, which takes the same two inputs — the price and your probability — and returns the fraction of bankroll that maximises long-run growth. Most bettors then take a quarter or a half of that.

• Expected Value in Sports BettingThe one number that decides whether a bet is worth making — and why it says nothing at all about whether this particular bet wins.11 min read
• The Kelly Criterion, Explained Without the CalculusThe mathematically optimal stake — and the reason almost nobody who understands it bets the full amount.10 min read
• Player Props: Why They Cost More Than You ThinkThe fastest-growing bet type is also the most expensive one on the board. What the margin actually is, and the one place the price is genuinely soft.10 min read

• Kelly Criterion CalculatorThe stake your edge justifies, at full Kelly or a safer fraction of it.
• Betting Edge CalculatorYour edge in probability points, and why that is not the same as EV.
• Push-Adjusted EVEV on a market where a push is a real possibility.
• No-Vig CalculatorStrip the bookmaker margin out of a market to see the fair price behind it.