The Prediction Market Expected Value Calculator is a free online tool designed for Polymarket and Kalshi traders who want to make data-driven decisions instead of emotional bets. This calculator shows whether a market is overpriced or underpriced based on your own probability estimate.
By entering the YES or NO price, your estimated true probability, market fees, and planned investment amount, you can instantly see your expected profit or loss, expected return on investment, and break-even probability. This helps you avoid negative-expectation trades and focus only on positions that offer a mathematical edge.
This tool is useful for beginners learning how prediction market pricing works and for advanced traders who want to quickly validate trades before risking capital.
Instantly check if a Polymarket or Kalshi trade is statistically worth taking before risking your money.
This calculator shows the statistical outcome if the same trade were repeated many times. It does not predict the future. It evaluates whether the odds justify the risk.
How This Calculator Works?
Prediction markets convert real-world events into tradable probabilities. A YES price of $0.63 means the market believes there is a 63 percent chance the event will happen. But markets are often wrong.
This calculator compares three things:
• The current market price
• Your personal estimated probability
• The amount you plan to invest
It then applies expected value formulas to calculate whether the trade has a positive or negative statistical edge.
The calculator computes:
• Implied probability from market price
• Break-even probability needed to not lose money
• Expected profit or loss for your trade size
• Expected ROI percentage
• Risk-to-reward ratio after fees
If your estimated probability is higher than the break-even probability, the trade has a positive expected value. If it is lower, the trade is mathematically unfavorable.
This removes guesswork and replaces it with clear numbers.
How This Calculator Helps Traders?
Most prediction market losses happen not because traders are wrong, but because they enter trades with negative expected value.
This calculator helps you:
• Avoid overpriced markets
• Identify underpriced opportunities
• Understand what probability you must be right at to make money
• Control risk before entering a trade
• Compare multiple markets objectively
• Think like a trader instead of a gambler
Instead of asking “Do I feel this will happen?”, the calculator forces the right question:
“Am I being paid enough for the risk I am taking?”
Over time, consistently using expected value tools is what separates profitable traders from random bettors.