Prediction Market Calculators

Odds converter and probability calculator

Prediction markets like Polymarket display prices in cents (where 73¢ = 73% implied probability), while Kalshi often uses percentages, and traditional sportsbooks use American odds, like +150 or -200. Our odds converter translates all formats so you can compare opportunities across platforms.

When you’re comparing the same market across Polymarket, Kalshi, and sportsbooks, each platform speaks a different language. You might see 67¢ on Polymarket, 33% on Kalshi, and -200 on a sportsbook – but which price is the best price? This calculator removes the mental math and lets you see implied probabilities at a glance. 

Arbitrage calculator

Arbitrage happens when you can buy all possible outcomes of an event across different platforms for less than $1 total, locking in a profit regardless of what happens. You’re literally betting on both sides – “Yes” on one platform and “No” on another. However, you also need to factor in the trading fees. Our arbitrage calculator accounts for platform-specific fees so you can see your true net profit.

Why fees matter

Platform fees can turn a 3% gross arbitrage into a 1-2% net return – or even a loss. Polymarket US charges 0.01% on trades, Kalshi charges approximately 0.7%, and Polymarket International charges 2% on net winnings. On a $1,000 arbitrage, you might pay $4-20 in fees depending on which platforms you’re using. Always calculate your net return after fees before committing capital.

Remember that smaller markets often have better arb opportunities because they’re less watched, but liquidity can be thin. The calculator is intended to help you identify the opportunity, but you’ll need to check if there’s enough market volume to make it worthwhile to execute the trade.

Multi-market comparison: (Polymarket vs. Kalshi)

A big complaint for prediction markets is the constant “checking markets, comparing prices, and calculating stakes manually. Our multi-market comparison tool solves this by allowing you to input the same market from Kalshi, PredictIt, Robinhood and Polymarket. If Trump to win is trading at 68¢ on Polymarket but 32% on Kalshi for “No,” you want to know which side offers better value while calculating the fees.

Expected value (EV) calculator

Input the current market price, your estimated actual probability, and your stake size. The calculator shows your expected value in both percentage and dollar terms. If the EV is positive, your trades will be mathematically profitable over time, even if you lose some individual bets. Use this to evaluate whether betting on high-probability events at 95¢+ is worth it (usually low EV due to capital lockup), or whether longshots priced at 8¢ might be undervalued. Remember: EV requires accurate probability estimates, so this tool is only as good as your research and analysis.

Kelly Criterion calculator

The Kelly Criterion answers a crucial question: even when you’ve found a +EV bet, how much of your bankroll should you actually risk? Bet too little and you’re not maximizing your edge; bet too much and you risk significant drawdowns. The Kelly formula calculates the optimal fraction of your bankroll to stake based on your edge and the odds, maximizing your long-term growth rate. It’s the mathematical answer to “how aggressive should I be?”

Example of a practical application

Input your estimated edge (the difference between your probability and the market’s probability) and the odds you’re getting. The calculator shows what percentage of your bankroll to stake. For example, if you have a 5% edge on a 60¢ market, full Kelly might suggest risking 12% of your bankroll – but most traders would use half-Kelly (6%) to reduce the chance of significant drawdowns. Use this for every non-arbitrage bet to ensure you’re sizing positions appropriately.

Calculate your breakeven point

This calculator answers a fundamental question: what win rate do you need to be profitable at these odds? If you’re consistently betting at 65¢ (implied probability of 65%), you need to win more than 65% of the time to show a profit. This tool instantly shows the break-even threshold so you can honestly assess whether your win rate justifies your betting activity.

Use this calculator to evaluate your historical performance and whether you’re actually profitable. If you’ve been betting an average price of 70¢ but only winning 67% of the time, you’re losing money even though your win rate seems impressive. Compare your actual win rate against the break-even rate for the odds you typically take.