Prediction market profit calculator (payout, breakeven & position size)
Stake, entry price and exit in; profit, ROI, breakeven and a sensible position size out.
How to use it: choose Yes or No, enter how much you'd spend and your bankroll, then drag the entry price, your target exit (or 100¢ if you hold to the end) and your own estimate of the true probability. The calculator shows profit, return, breakeven and a suggested size.
The calculator doesn't include platform fees. On Kalshi, use the odds converter with the fee option ticked to see the fee for a given trade. "Kelly" sizing is a textbook formula; most traders use half of it or less.
How to read the results
- Profit and ROI: what you'd make if the price reaches your target.
- Breakeven: the price you need just to get your money back.
- Kelly sizing: a formula that suggests how much of your bankroll to use given your edge. If your estimate isn't better than the price, it suggests zero, and that's the honest answer.
Frequently asked questions
How is profit calculated on a prediction market?
Profit = (exit price − entry price) × number of contracts, minus fees. If you hold to the end, the exit price is $1 if you're right and $0 if you're wrong.
What is the Kelly criterion?
A formula for sizing bets based on your edge and the price. It maximises long-run growth in theory but is aggressive in practice, so many traders use a fraction of it.
