Your estimatevsMarket price
Expected Value Calculator
Enter your own probability estimate and the contract's market price to see the edge, in both dollars and percentage points, and the price at which that edge disappears.
Positive edge: +8.0 points, +$0.08 per contract
Positive EV means buying this side is profitable on average if your probability estimate is right -- it doesn't guarantee this particular contract wins.
EV per contract
$0.08
EV per $100 staked
$15.38
~192 contracts
Price where EV = 0
60.0¢
i.e. your own probability estimate
| Your estimate | Market price | |
|---|---|---|
| Probability | 60.00% | 52.00% |
| Edge | +8.0 pts | — |
How this is calculated
EV per contract = your probability estimate − the market's price, both as dollars. At the default 60% estimate against a 52¢ price, that's $0.08 -- a 8.0-point edge. Move the price up to exactly 60¢ and the edge disappears entirely: the breakeven price is always just your own stated probability, expressed in cents.
EV per $100 divides EV per contract by the price and multiplies by 100, which is the same as saying: how much do I expect to make for every $100 I put at this price. At 52¢, $100 buys about 192 contracts, so the same $0.08-per-contract edge becomes $15.38 on a $100 stake.
This is not the same thing as buying a real prediction-market contract. It ignores fees, spread between what you can buy and sell at, and the fact that your own probability estimate is itself uncertain. See the payout calculator for a fee-inclusive version, and the arbitrage calculator for the one case where you don't need your own probability estimate at all.
Frequently Asked Questions
Why is expected value just 'your probability minus the price'?
Because a contract pays exactly $1 if you're right and $0 if you're wrong, so the whole payoff structure collapses to one line: EV = p x $1 + (1-p) x $0 - price = p - price. On the default numbers -- your estimate at 60%, the market at 52¢ -- that's $0.08 per contract. There's no separate 'stake' or 'odds' term to track the way there is in a sportsbook payout, which is what makes prediction-market EV unusually clean to compute.
What does 'EV per $100' add that EV per contract doesn't?
It puts every price on the same footing. A contract at 5¢ and a contract at 90¢ have very different EV-per-contract numbers just because you can buy 20x as many of the cheap ones with the same money -- EV per $100 divides that out, so you can compare the actual return on capital across two completely different prices or markets.
Is this the same 'expected value' from a statistics class?
Same underlying concept -- a probability-weighted average of outcomes -- applied to a specific payoff shape. General statistics EV covers any distribution of outcomes and payouts; this page is the narrow case where there are only two outcomes and the payout is fixed at $1 or $0, which is what every prediction-market contract looks like.
If my estimate has positive EV, should I actually make the trade?
Positive EV is necessary but not sufficient. It tells you the trade is profitable on average IF your probability estimate is right -- it says nothing about how confident you should be in that estimate, how much of your bankroll to risk, or whether fees eat the edge. The Kelly criterion calculator handles the sizing question once you've found an edge here.
Why would the market's price ever be 'wrong'?
Markets aggregate opinions, not certainty -- a price reflects what traders collectively are willing to pay, which can lag new information, be thin on low-volume contracts, or simply reflect a different (and possibly better) information set than yours. A positive edge here isn't proof the market is wrong; it's a bet that your information or analysis is worth more than the crowd's in this specific case.
SidebySideCalc's prediction-market calculators apply standard odds, probability, and bankroll-sizing math to the numbers you enter -- they are not trading advice. Prediction markets carry real risk of loss and may be restricted or unavailable in some jurisdictions; nothing here names or endorses a specific trading venue.