Prediction Market Calculators13 free Kalshi and Polymarket calculators for odds, expected value, arbitrage and fees
Convert odds, check a trade’s expected value and break-even, compare apps after fees, find arbitrage and size your bets; every answer updates as you type.
Work out a trade before you place it
Convert odds, check a trade’s expected value and break-even, compare apps after fees, find arbitrage and size your bets. Every answer updates as you type.
Odds converter
A prediction market price in cents is the market’s chance in percent. Type odds in any format to see the others.
- Profit on a $100 bet
- $100
- How often it wins
- About even
- Risk
- Medium
Expected value (EV)
What a trade makes on average if your probability is right. Positive EV pays off over many trades, even though single trades lose.
No fees.
- EV per $1
- +$0.10
- Your edge
- +5 pts
- Price
- 50¢
- Price after fees
- 50¢
- Fees
- $0.00
- If it wins
- +$100.00
- If it loses
- −$100.00
Break-even probability
The win rate a price needs before it makes money. If you keep buying at 65¢, you have to win more than 65% of the time, plus fees.
No fees.
- Price
- 55¢
- Fees a contract
- 0¢
- Edge you need
- 0 pts
Position P&L
Profit or loss on contracts you buy and later sell, after the fee on each trade.
Kalshi: 0.07 × contracts × price × (1 − price), rounded up to the cent (at most 1.75¢ a contract, at 50¢). On orders that trade right away (taker orders) on most markets; some markets charge less, and resting orders pay less or nothing. No fee at settlement.
- Cost
- $45.00
- Sale proceeds
- $65.00
- Gross profit
- +$20.00
- Fee to buy
- $1.74
- Fee to sell
- $1.60
- Total fees
- $3.34
Hedging
Lock in a result by buying the same number of contracts on the other side, so you’re paid the same whichever side wins.
- Your position
- 1,000 YES at 40¢, $400.00
- Hedge
- Buy 1,000 NO at 35¢, $350.00
- If YES wins
- +$250.00
- If NO wins
- +$250.00
Compare apps
The same market’s YES price on each app, and what each side costs there after fees. NO costs 100¢ minus YES.
| App | YES | After fees | NO | After fees |
|---|---|---|---|---|
| Polymarket US best NO | 52¢ | 53.73¢ | 48¢ | 49.73¢ |
| Kalshi best YES | 48¢ | 49.75¢ | 52¢ | 53.75¢ |
| Robinhood | 50¢ | 52¢ | 50¢ | 52¢ |
| PredictIt | 51¢ | 53.63¢ | 49¢ | 51.63¢ |
Arbitrage finder
Buy YES on one app and NO on another for less than the $1 a pair pays, and you profit whichever side wins. Check there’s enough volume at these prices first.
- Buy YES
- Kalshi at 48¢, 49.75¢ with fees
- Buy NO
- Polymarket US at 48¢, 49.73¢ with fees
- A pair costs
- 99.48¢
- A pair pays
- 100¢
- Contracts on each side
- about 1,005.21
Kelly criterion
How much of your bankroll to bet on a trade with an edge: the share that grows it fastest over time. Many traders bet a quarter of that to soften the swings.
- Your edge
- +10 pts
- Full Kelly
- 20.00%
- Quarter Kelly
- 5.00%
Vig (overround)
How far a market’s YES and NO prices add up past 100¢: the house edge. Lower vig means fairer prices.
- YES + NO
- 104¢
- Fair YES price
- 50¢
- Fair NO price
- 50¢
Parlays
Independent events combined into one bet: it pays only if every leg hits, and the chance is every leg’s chance multiplied.
- Market’s chance
- 42.00%
- Your chance
- 48.75%
- Profit if it hits
- +$138.10
- Expected value
- +$16.07
- Expected return
- +16.07%
- Your edge
- +6.75 pts
Bankroll simulator
100 simulated runs of even-money bets (buying at 50¢), each a fixed share of your bankroll at the time, to show how a real edge can still run dry.
- Best run
- $59,087.20
- Risk of ruin
- 0%
Fees by app
Each app’s trading fee from its own published schedule, checked Oct 2, 2026 (Kalshi’s Sep 23, 2026). Deposit and withdrawal fees are in our guide to prediction market fees.
| App | Trading fee | When it’s charged |
|---|---|---|
| KalshiKalshi fee schedule | 0.07 × contracts × price × (1 − price), rounded up to the cent (at most 1.75¢ a contract, at 50¢) | On orders that trade right away (taker orders) on most markets; some markets charge less, and resting orders pay less or nothing. No fee at settlement. |
| Polymarket USPolymarket US fee schedule | 0.0695 × contracts × price × (1 − price), rounded to the nearest cent (at most 1.74¢ a contract, at 50¢) | On taker orders; resting (maker) orders earn a rebate. |
| RobinhoodRobinhood event contracts | A commission of 10% × price × (1 − price) a contract, at most 1¢ and rounded up to the cent, plus an exchange fee of up to 1¢ a contract | When you open and when you close. Assumes no Robinhood Gold (it halves the commission) and the full exchange fee. |
| FanDuel PredictsFanDuel Predicts payouts | 2¢ a contract | At checkout, win or lose, and the same again to cash out early. Nothing at settlement. |
| PredictItPredictIt fee announcement | 10% of the profit on a winning trade | Only on winning trades, when they win or you sell at a profit. No withdrawal fee. |
| Gemini PredictionsGemini Predictions fee schedule | 0.07 × contracts × price × (1 − price), rounded up to the cent (at most 1.75¢ a contract, at 50¢) | On taker orders; resting (maker) orders pay a quarter of the rate. |
| ForecastEx (through Interactive Brokers)Interactive Brokers event contract pricing | 1¢ a contract | Each trade. Interactive Brokers charges no commission; the fee is the exchange's. |
| DraftKings PredictionsDraftKings Predictions fee disclosure |
| Each side, opening or closing. |
| OG PredictionsOG fees and limits |
| On taker orders, to open or to close early; resting (maker) orders pay a quarter of the rate. Waived at settlement. |
| Crypto.comCrypto.com prediction trading |
| On taker orders; resting (maker) orders pay a quarter of the rate. Waived at settlement. |
| Fanatics MarketsFanatics Markets fee disclosure | Up to 2¢ a contract, less on prices near 0¢ and 100¢, rounded up to the cent | Each matched order, buying or selling. |
| Polymarket (international)Polymarket fees |
| On taker orders; makers pay nothing. |
What fees cost on one trade
The same trade on every US app: what you pay in fees, and what you’re left with, if you hold the contracts until the market settles.
| App | Fees | Net result | Fees as % of profit |
|---|---|---|---|
| ForecastEx (through Interactive Brokers) cheapest | $2.00 | +$98.00 | 2.0% |
| Polymarket US | $3.48 | +$96.52 | 3.5% |
| Kalshi | $3.50 | +$96.50 | 3.5% |
| Gemini Predictions | $3.50 | +$96.50 | 3.5% |
| OG Predictions (most markets) | $3.50 | +$96.50 | 3.5% |
| Crypto.com (sports and prediction markets) | $3.50 | +$96.50 | 3.5% |
| Robinhood | $4.00 | +$96.00 | 4.0% |
| FanDuel Predicts | $4.00 | +$96.00 | 4.0% |
| DraftKings Predictions (CME markets) | $4.00 | +$96.00 | 4.0% |
| DraftKings Predictions (DKeX and Crypto.com markets) | $4.00 | +$96.00 | 4.0% |
| OG Predictions (crypto, FX, commodity and index markets) | $4.00 | +$96.00 | 4.0% |
| Crypto.com (crypto, FX, commodity and index markets) | $4.00 | +$96.00 | 4.0% |
| Fanatics Markets | $4.00 | +$96.00 | 4.0% |
| PredictIt | $10.00 | +$90.00 | 10.0% |
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.
- Is prediction market arbitrage legal?
In the US, trading on a CFTC-regulated exchange such as Kalshi or Polymarket US is legal where the app operates, and buying opposite sides of the same question on two of them is ordinary trading: no rule forbids holding both. Each app’s own terms still apply, and your profit is taxable. We’re not lawyers; this isn’t legal advice.
- How are Kalshi fees calculated?
On orders that trade right away, Kalshi charges 0.07 × the number of contracts × the price × (1 − the price), with the price in dollars, and your balance moves in whole cents, so the cost rounds up. The fee is largest at a 50/50 price and shrinks toward either end. Some markets charge less, resting orders pay less or nothing, and there’s no fee at settlement. The fee table shows every app’s.
- How are Polymarket US fees calculated?
Taker orders pay 0.0695 × the number of contracts × the price × (1 − the price), rounded to the nearest cent; resting (maker) orders earn a rebate instead. Like Kalshi’s, the fee peaks at a 50/50 price.
- Why do arbitrage opportunities disappear so fast?
Traders and bots watch the same prices, so a gap closes within seconds or minutes, and fees often eat what’s left. A price is also only good for the contracts on offer at it: a large order walks up the order book and pays more. Check the depth before you trade, and use the arbitrage finder with each app’s fee.
- What is expected value in a prediction market?
Your own estimate of the chance something happens, times what a contract pays, minus what it costs. If you think an outcome is more likely than the price implies, buying it has positive expected value. The expected value calculator does it after fees.
- How do I convert a prediction market price to American odds?
For a favorite priced at p (in dollars), American odds are −100 × p ÷ (1 − p); for an underdog, +100 × (1 − p) ÷ p. So a 75¢ contract is about −300 and a 25¢ one about +300, before fees. The odds converter does every format at once.
- What is the Kelly criterion?
A formula for how much of your bankroll to put on a trade when you think the price is wrong: the bigger your edge and the better the odds, the bigger the stake. Many traders use a fraction of it, such as half Kelly, because full Kelly swings hard when your estimate is off.
- Are these calculators free?
Yes. They run in your browser, with no sign-up and nothing to install, and the numbers you enter stay on your device.
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