Polymarket ROI Calculator
Calculate expected ROI, optimal position size with Kelly Criterion, and break-even win rates for your Polymarket trades.
Example: Market says 60%, you think it's 65% → your edge is +5%
Note: calculations shown before the 0.5% taker fee that applies on trades copied via Polyfollow. Maker orders incur no fee. No subscription, no performance fee.
Understanding the Metrics
Expected ROI
Average return you'd expect if you made this trade many times. Positive = profitable edge, negative = losing proposition. Formula: (Your Prob x Win) minus (1 - Your Prob)
Kelly Criterion
Optimal position size to maximize long-term growth while minimizing risk of ruin. Many traders use "half Kelly" (50% of suggested) to reduce volatility. Learn more in our copytrading guide.
Break-Even Win Rate
Minimum accuracy needed to not lose money at this price. If the market is at 60%, you need >60% accuracy to profit. Your edge should push you above this threshold. See Polymarket fees for how taker costs affect your effective break-even.
ROI Calculator FAQ
What is expected ROI on Polymarket?
Expected ROI (return on investment) measures the average return you would get if you placed this trade many times. It is calculated as: (Your estimated probability x Net payout) minus (1 - Your estimated probability). A positive expected ROI means you have an edge over the market price. A negative expected ROI means you are paying too much for the shares.
How does the 0.5% Polyfollow fee affect expected value?
When copying trades via Polyfollow, a 0.5% builder fee applies to each taker order. This reduces your net payout slightly. For example, on a $100 trade with a 65% market price and +5% edge, the fee costs $0.50, reducing your profit from $53.85 to $53.35. Maker orders incur no fee. There is no subscription and no performance fee on profits.
What is the Kelly Criterion and should I use it?
The Kelly Criterion is a formula that tells you the optimal fraction of your bankroll to risk on a trade given your edge and the odds. Full Kelly maximizes long-term growth but can cause large drawdowns. Most professional traders use half Kelly (50% of the suggested size) to reduce volatility while still capturing most of the growth advantage.
What does break-even win rate mean?
Break-even win rate is the minimum accuracy you need at a given market price to avoid losing money. If a share costs $0.60, you need to be right more than 60% of the time to profit. If you believe your true probability is above the break-even rate, the trade has positive expected value.
Ready to Trade with an Edge?
Copy traders who consistently find positive expected value opportunities on Polymarket. Use their edge instead of searching for your own.