Free Expected Value calculator for binary YES-contracts on Polymarket: calculate EV, edge, and optimal position size using Kelly Criterion — no sign-up required.

Free calculator, paid tools in dashboard

Expected value for prediction markets.

This page is the free public calculator in EdgeVisor. It closes one SEO cluster with multiple phrasings: calculate EV, understand the formula, compare your estimate with the market, and size a binary YES trade with Kelly. The broader paid working tools stay inside the registered dashboard.

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One structure for the full cluster

The page follows the exact order that solves the user job: formula, plain-language interpretation, input table, calculator, long-tail FAQ, and finally a CTA into the main EdgeVisor tool.

Block 1 — Scientific explanation

The formula behind expected value

For a binary YES contract priced at c, with your estimated win probability p and stake S, the expected value of buying YES can be written in a compact way that matches prediction-market payoff mechanics.

EV = S * (p - c) / c Edge = (p - c) * 100 Kelly for YES = (p - c) / (1 - c), if p > c; otherwise 0

The key idea is simple: the market price is an implied probability. If your probability is materially above that price, the contract may be underpriced. EV tells you the dollar attractiveness; Kelly translates that edge into a bankroll fraction.

Block 2 — Plain-language explanation

What this means in real trading language

If the market says YES is 62% but your estimate is 75%, you think the market is pricing the event too cheaply. That disagreement is the raw edge.

Market probability The crowd's current price for the event.
Your estimate Your own belief after research or modeling.
Decision output EV, edge, and Kelly tell you whether the setup is attractive and how aggressively to size it.

Block 3 — Input table

Every query variant eventually needs the same operational answer: what to enter, where it comes from, and what the calculator returns.

Parameter What you enter Where it comes from
Market probability 0–100% YES price Polymarket, Kalshi, or another binary exchange quote
Your estimate 0–100% true probability Your research, model, or judgment
Stake $ amount at risk Your bankroll plan
EV Auto-calculated Dollar value of the edge at the chosen stake
Edge Auto-calculated Difference between your probability and the market price
Kelly fraction Auto-calculated Suggested bankroll fraction for a binary YES contract under Kelly assumptions

Block 4 — EV calculator

This is the instrument itself: market probability, your estimate, and stake in one place. The output updates instantly and stays venue-agnostic for binary YES contracts.

Tool input

Prediction market EV quick check

Use the sliders for the two probabilities and enter a stake. The page calculates EV, edge, and Kelly in real time.

Cheap YESExpensive YES
Low convictionHigh conviction
Output

Trade readout

The calculator returns three numbers because they answer three different decisions: is it favorable, how large is the disagreement, and how hard should sizing lean into it.

Expected value
+$20.97
Positive EV means the trade is favorable in expectation if your estimate is calibrated.
Edge over market
+13.0 pp
Your estimate is 13.0 percentage points above the market.
Kelly fraction
34.2%
Kelly is shown as a fraction of bankroll for a YES-only binary contract.
Positive signal

Your estimate is above the market, so the contract looks favorable on this simplified EV model.

Raw Kelly exceeds 100% of bankroll. The displayed value is capped at 100% because anything above that indicates an oversized position under the naive model.
Constraint: this widget models a binary YES payoff only. It does not include fees, slippage, correlation, or execution limits.
Use case: treat this as an entry sanity check, then move into EdgeVisor Tool if you want a structured bull/bear read on a real market URL.

Block 5 — Long-tail FAQ

The FAQ captures the long-tail phrasing that usually surrounds EV search intent and reinforces the topical cluster without splitting it into multiple pages.

What is positive EV in a prediction market?

Positive EV means your estimated probability is high enough relative to the market price that buying YES is favorable in dollars on average. It is not a guarantee on a single trade.

How is EV different from Kelly?

EV answers whether the setup is attractive for the chosen stake. Kelly answers how much of bankroll to allocate under stronger assumptions about calibration, repeatability, and independence.

Can I use this for Kalshi?

Yes, for binary YES-style contracts. You still need to adjust separately for platform-specific fees, rounding, and settlement details.

Why does Kelly show 0% when my estimate is below the market?

This page uses the canonical YES-side Kelly formula. If your estimate is not above the market price, there is no positive YES edge on this model, so Kelly is shown as 0%.

What if I want a real market signal instead of a manual calculator?

That is exactly where EdgeVisor Tool comes in: paste a Polymarket URL and get a structured preview with direction, confidence, context, and liquidity warnings.

Block 6 — CTA to EdgeVisor Tool

Calculated EV already? Move from math to market context.

Use this calculator to validate a setup. Then open /tool, paste a Polymarket link, and get a structured read with quick directional context, confidence framing, and execution caveats.

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Educational only. This calculator does not give financial advice and does not execute trades. Prediction markets involve real risk, including complete loss of the stake. Always account for fees, slippage, and uncertainty in your own probabilities.