Polymarket Odds Calculator — Probability & Payout
Free Polymarket odds calculator. Convert market prices ($0.65) to implied probability (65%), calculate bet payout, hedge positions, and find arbitrage opportunities across prediction markets.
Prediction markets are taxed as gambling income in many jurisdictions. Polymarket charges 2% on winnings; UMA disputes can affect resolution. US-restricted (use VPN at own legal risk).
How to use Polymarket Odds Calculator — Probability & Payout
This Polymarket Odds Calculator turns a prediction-market share price into the numbers you actually need to bet. Because each winning YES or NO share redeems for exactly $1 in USDC, the YES price doubles as the implied probability — $0.65 means the market prices the event at 65%, and the NO price is simply 1 − YES. From your bet size and the side price it computes shares purchased (bet ÷ price), payout if win, profit if win, and loss if lose, then restates the same price as decimal, American, and fractional odds.
The edge analysis is where it earns its keep. You supply your own YES probability estimate, and the tool compares it to the market's implied probability to compute expected value = (true prob × profit) − (loss prob × stake), plus your percentage edge and a +EV / Negative-EV rating. It also runs the Kelly criterion, f = (b·p − q) ÷ b, to suggest the bankroll fraction to stake, and an optional hedge calculation that buys the opposite side at a later price to lock profit across both outcomes.
Input guide and assumptions
Bet Side toggles YES or NO; YES Market Price (USD, 0–1) is the share price you pay; Bet Size (USD) is your stake. Your YES Probability Estimate (%) feeds the EV, edge, and Kelly math, this is your forecast, not the market's. The optional Hedge at Future YES Price field models laying off the bet on the opposite side later: leave it blank to skip hedging entirely. Built for binary Polymarket-style markets where YES and NO shares each settle at $1.
Prices must sit strictly between 0.01 and 0.99, and probabilities between 0 and 100%, values outside that show an "enter valid inputs" message. The tool models a single binary market and assumes shares redeem at exactly $1; it does not deduct Polymarket's 2% fee on winnings, gas, or slippage, so treat profit and EV as gross. For sizing discipline check the suggested stake against our <a href="/kelly-calculator/">Kelly criterion calculator</a>, and spot cross-market mispricings with the <a href="/arbitrage-calculator/">arbitrage calculator</a>.
How to interpret results correctly
The hero number is Profit If You Win, your shares minus your stake, with the decimal-odds multiplier, EV%, and a rating (Strong +EV, Positive EV, Marginal, or Negative EV) underneath. Treat that rating as the real verdict: it compares your YES probability estimate against the market price, not just the headline payout. A large profit on a 0.10 long shot still earns a Negative EV badge if your edge does not justify the odds.
Below the hero, read Implied probability as the market's price-as-percentage, then Your edge vs market, your estimate minus the implied probability. Positive edge is the whole case for the bet. Cross-check Kelly bet size (% bankroll) against a disciplined stake plan; if Kelly reads near zero or negative, the market has no exploitable gap. For pure position sizing, pair this with the <a href="/kelly-calculator/">Kelly criterion calculator</a>.
Practical scenarios and planning workflow
Pricing a directional bet is the core use: enter the YES market price (say 0.65), your own YES probability estimate, and a stake. The calculator returns Shares purchased, Payout if win, Profit if win, Loss if lose, and the EV that says whether your view beats the crowd. Flip Bet Side to NO when you think the favorite is overpriced; the engine recomputes shares against the 1 − YES price automatically.
Locking a profit is the second workflow: fill the optional Hedge at Future YES Price field after the market has moved in your favor. It shows the Hedge bet required on the opposite side and the Locked profit (both outcomes), so you can size a hedge that pays the same whether YES or NO resolves. Before committing real size, sanity-check stake fractions with the <a href="/position-size-calculator/">position size calculator</a>.
Risk and execution checklist
- Before betting: 1) Confirm the YES price is the live executable price, not a stale mid. 2) Set your YES probability estimate from independent research, never from the market price you are trying to beat. 3) Check that Your edge vs market is comfortably positive, not within a rounding error. 4) Read the Kelly bet size and stake at most a fraction of it, since full Kelly is brutally volatile on binary outcomes.
- Before hedging: 1) Enter the current opposite-side price in the hedge field and confirm Locked profit (both outcomes) is genuinely positive. 2) Account for the 2% Polymarket fee on winnings, which this snapshot does not subtract. 3) Verify market liquidity can fill both your entry and your hedge without moving the price. 4) Re-run the numbers if the YES price drifts before you place either leg.
Common mistakes to avoid
- The biggest mistake is anchoring your probability estimate to the market price itself, then your edge is mechanically near zero and EV is meaningless. The whole point is an independent forecast. The second is staking full Kelly: on a binary market a single loss at full Kelly can erase a large share of bankroll, so most disciplined bettors use a quarter or half of the Kelly bet size this tool reports.
- Another error is ignoring fees and resolution risk. The Profit if win row is gross; Polymarket takes 2% on winnings and UMA disputes can delay or flip resolution, so a thin +EV edge can vanish. Finally, do not confuse the Implied probability (price) with your true probability, the difference is the edge, and treating them as the same number defeats the calculator's purpose entirely.
Performance benchmarks and expectation ranges
On liquid election or sports markets, edges over the price are usually small: a genuine 2–5% gap between your estimate and the Implied probability is already a strong, tradeable signal, and anything claiming a 20%+ edge on a heavily traded market almost always means a wrong probability estimate. Decimal odds of 1.54 on a 0.65 favorite and around 2.00 on a coin flip are the everyday reference points.
Kelly bet size on realistic edges rarely exceeds single-digit percent of bankroll; a 4% edge at decimal odds near 1.5 yields a Kelly fraction in the low single digits, which is why fractional Kelly is the norm. Expect American odds around −186 on a 0.65 YES and roughly even-money near 0.50. Treat any EV% above +10% (the Strong +EV band) on a deep market with healthy skepticism.
Execution templates you can reuse
Workflow: 1) Form a probability estimate before opening the market, then enter the live YES price and your stake. 2) Read Your edge vs market and EV%; proceed only if both are clearly positive. 3) Take the Kelly bet size, halve or quarter it, and set that as your stake. 4) Place the bet on the chosen side. 5) Log the entry price, your estimate, and the EV the tool showed.
To manage the position: 1) Watch the market price as new information arrives. 2) When it moves your way, enter the current opposite-side price in the hedge field. 3) If Locked profit (both outcomes) is positive after the 2% fee, place the hedge to bank a guaranteed return. 4) Otherwise hold to resolution. Compare the risk-reward of holding versus hedging with the <a href="/risk-reward-calculator/">risk/reward calculator</a>.
Data hygiene and model maintenance
Your probability estimate is the only input that is truly yours, keep it honest and dated. Re-enter the YES price each session, because Polymarket prices move continuously and a number from yesterday makes every downstream row (edge, EV, Kelly) wrong. When fresh news drops, update your estimate first, then re-read whether the edge still survives the new market price.
Maintain a betting log: market, date, entry YES price, your estimate, the EV% and Kelly fraction shown, your actual stake, and the resolved outcome. Over dozens of bets, comparing realized return against the modeled EV reveals whether your probability estimates are genuinely calibrated or systematically over-confident, the single most important hygiene check for any prediction-market bettor.
Final validation before capital deployment
Sanity-check the core arithmetic yourself: Shares purchased equals stake divided by your side's price, and each share resolves to $1, so Payout if win equals shares and Profit if win equals payout minus stake. Implied probability is just the side price times 100. If those tie out, the headline figures are trustworthy; convert any stake or share amounts you doubt with the <a href="/converter/">crypto converter</a>.
Validate the EV with the textbook formula: EV equals your side's true probability times Profit if win, minus (1 − that probability) times Loss if lose. Your edge vs market is simply your probability minus the implied probability, and Kelly follows f = (b·p − q) / b with b = decimal odds − 1. If EV is positive but edge is zero, your two probability figures are accidentally equal, fix the estimate before trusting the verdict.
Authoritative sources
Frequently asked questions
How do Polymarket prices work?
Polymarket uses a Conditional Token Framework where each YES and NO share resolves to $1 if correct, $0 if wrong. Prices float between $0.01 and $0.99 based on order book trading and represent the market's implied probability - a YES share at $0.65 means the market thinks there is a 65% chance the event happens. You buy and sell at any time before resolution.
How to convert Polymarket odds ($0.65) to probability?
Direct conversion: $0.65 = 65% implied probability. To convert to American odds: positive odds = (1/price - 1) * 100, so $0.65 -> +54; negative odds = -100 / (1/price - 1), so $0.75 -> -300. Decimal odds = 1 / price, so $0.65 -> 1.54. Always subtract Polymarket's effective spread (typically 1-3 cents on liquid markets) before computing true edge.
What does "expected value" mean for prediction markets?
Expected value (EV) = (your probability * payout) - (1 - your probability) * cost. If you think the true probability is 75% and you buy YES at $0.65, EV per dollar = (0.75 * $1.00) - (0.65 * $1.00) = $0.10, a 15.4% edge. Only bet when EV is positive AND you have a defensible reason your estimate beats the market - otherwise you are paying the spread to gamble.
Can I hedge a Polymarket bet?
Yes - sell some of your YES shares back into the order book before resolution to lock in profit, or buy NO shares to neutralize. For real-world hedges, mirror exposures: hedge a "Trump wins 2024" YES bet by shorting equity sectors that would benefit, or hedge a crypto-related market with a perp position. Note that liquidity dries up sharply near resolution, so plan exits in advance.
Is Polymarket legal in the US?
Polymarket settled with the CFTC in 2022 and officially blocks US users via geo-fencing and KYC. After the November 2024 election it announced plans to re-enter the US under proper licensing, and as of 2026 it operates a US-compliant version (Polymarket US) for residents in approved states. Using a VPN to bypass restrictions on the offshore version violates terms of service and may have CFTC enforcement implications.
How are Polymarket winnings taxed?
In the US, prediction market profits are typically taxed as gambling winnings (ordinary income, no capital gains treatment) and reported on Schedule 1. You can deduct losses only if you itemize and only up to winnings (Section 165(d)). For frequent traders, professional gambler status under Section 162 may allow business-expense treatment - but the bar is high. Always document each market's entry, exit, and outcome.
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