Prediction Market Calculators14 free Kalshi and Polymarket calculators for odds, expected value, arbitrage and fees
Convert odds, check a trade’s expected value and yearly return, compare apps after fees, find arbitrage and size your trades. Every answer updates as you type.
Odds and prices
What a price means: as odds in every format, without the house’s cut, and as a yearly return.
Odds converter
Type any number into one of the four boxes and the other three convert as you type. A prediction market price in cents is the market’s chance in percent.
- Price on Kalshi or Polymarket
- YES 50¢ · NO 50¢
- $100 of contracts
- pays $200, $100 profit
- How often it wins
- About even
- Risk
- Medium
A sportsbook’s two sides add up to more than 100%: the extra is its cut. Enter the other side’s odds to see this side’s fair chance and compare it with a prediction market’s price.
Odds conversion chart: every format from 1¢ to 99¢
| Price (chance) | American | Decimal | Fractional | $100 makes |
|---|---|---|---|---|
| +9900 | 100.00 | 99/1 | $9,900 | |
| +4900 | 50.00 | 49/1 | $4,900 | |
| +1900 | 20.00 | 19/1 | $1,900 | |
| +900 | 10.00 | 9/1 | $900 | |
| +567 | 6.67 | 17/3 | $567 | |
| +400 | 5.00 | 4/1 | $400 | |
| +300 | 4.00 | 3/1 | $300 | |
| +233 | 3.33 | 7/3 | $233 | |
| +186 | 2.86 | 13/7 | $186 | |
| +150 | 2.50 | 3/2 | $150 | |
| +122 | 2.22 | 11/9 | $122 | |
| +100 | 2.00 | 1/1 | $100 | |
| -122 | 1.82 | 9/11 | $82 | |
| -150 | 1.67 | 2/3 | $67 | |
| -186 | 1.54 | 7/13 | $54 | |
| -233 | 1.43 | 3/7 | $43 | |
| -300 | 1.33 | 1/3 | $33 | |
| -400 | 1.25 | 1/4 | $25 | |
| -567 | 1.18 | 3/17 | $18 | |
| -900 | 1.11 | 1/9 | $11 | |
| -1900 | 1.05 | 1/19 | $5 | |
| -4900 | 1.02 | 1/49 | $2 | |
| -9900 | 1.01 | 1/99 | $1 |
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¢
Annualized return
What a contract returns a year if you hold it until it settles: a 95¢ contract that pays $1 in 30 days is a 5.3% return, about 64% a year. Worth it only if the chance it wins is above its price, and above what cash would earn.
No fees.
- Cost a contract, with fees
- 95¢
- Pays if it wins
- 100¢
- Break-even chance
- 95.00%
- Chance it needs to beat 4.0% cash
- 95.31%
One trade
Before you buy: whether it’s worth it and the win rate it needs. After: what you made, and how to lock it in.
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
Across apps
The same market on Kalshi, Polymarket and the rest: where it’s cheapest after fees, and when buying both sides locks a profit.
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
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% |
Sizing and risk
How much to put on a trade with an edge, what a run of trades can do to a bankroll, and what combining events costs.
Kelly criterion
How much of your bankroll to put on a trade with an edge: the share that grows it fastest over time. Many traders use a quarter of that to soften the swings.
- Your edge
- +10 pts
- Full Kelly
- 20.00%
- Quarter Kelly
- 5.00%
Parlays
Independent events combined into one position: 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 trades (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%
Which calculator do I need?
- What does this price mean? The odds converter, and the vig calculator for a market’s two sides.
- Should I buy at this price? Expected value with your own chance, break-even without one, and the annualized return for a contract that settles months away.
- Where is it cheapest? Compare apps, then the arbitrage finder if the prices disagree.
- What did I make, and can I lock it in? Position P&L and hedging.
- How much should I trade? The Kelly criterion and the bankroll simulator.
How to read a prediction market price
On Kalshi, Polymarket and the other prediction market apps, a contract pays $1 if its outcome happens and nothing if it doesn’t, so its price in cents is the market’s chance in percent: 75¢ means 75%. Sportsbooks quote the same idea as American odds (−300), decimal odds (1.33) or fractional odds (1/3). The odds converter turns any one of them into the others, and its chart lists every format from 1¢ to 99¢.
A sportsbook’s two sides add up to more than 100%: at −110 on both sides each is 52.4%, together 104.8%, and the extra is the book’s cut. Enter the other side’s odds in the converter to take that cut out: −110 / −110 is a fair 50%, so a prediction market price under 50¢ on the same side is the better deal. The vig calculator does the same for a market’s YES and NO prices.
Is a trade worth it? Expected value, break-even and yearly return
A trade makes money over time only if the chance it wins is above what it costs. If you think something is 60% likely and it trades at 50¢, $100 buys 200 contracts: they pay $200 if it happens, so the trade’s expected value is 60% × $100 profit − 40% × $100 loss = +$20, before fees. Fees raise the bar: at 65¢ on Kalshi the taker fee of about 1.6¢ a contract means you have to win about 66.6% of the time to break even, not 65%.
High-priced contracts look safe but tie up money until they settle. A 95¢ contract that pays $1 in 30 days returns 5.3%, about 64% a year; the annualized return calculator shows that rate after fees and the chance the contract needs to beat cash. It’s worth buying only if it wins more than 95% of the time: one loss wipes out about nineteen wins.
After you buy: profit, loss and hedging
You don’t have to hold until a market settles. Sell when the price moves and the position P&L calculator shows what you made after the fee on each trade. To lock a result instead, buy the same number of contracts on the other side: if you hold 1,000 YES at 40¢ and YES is now 65¢, buying 1,000 NO at 35¢ costs $350, and you’re paid $1,000 whichever side wins, $250 more than the $750 both cost. The hedging calculator does the math for any price.
Comparing apps and finding arbitrage
The same question often trades at different prices on different apps. The compare apps calculator shows where each side is cheapest after that app’s fee, and the arbitrage finder checks whether buying YES on one app and NO on another costs less than the $1 the pair pays.
Fees decide most of these. YES at 48¢ on Kalshi and NO at 49¢ on Polymarket US cost 97¢ for a pair that pays $1, a 3¢ gap, but the two taker fees add about 3.5¢ a pair, so the trade loses money. The fee table lists every app’s schedule from its own published page, and the fee impact calculator shows what the same trade costs on each. Check the order book too: a price is good only for the contracts on offer at it.
How much to put on a trade
Even with an edge, trading too large can empty an account on a bad run. The Kelly criterion calculator gives the share of your bankroll that grows it fastest: if you think a 60¢ contract is 65% likely, full Kelly is 12.5% of your bankroll, half Kelly 6.25%. Many traders use a quarter or half, because full Kelly assumes your estimate is right. The bankroll simulator runs 100 sequences of trades so you can see how often a real edge still ends below where it started.
Combining events multiplies their chances: two legs at 70% and 60% hit together only 42% of the time. The parlay calculator shows the payout and, with your own chance for each leg, whether the combination has an edge.
Share a calculation
Every calculator has a Copy link button: the link opens the page with your numbers already in that calculator, so you can send a trade to someone else or keep it for later. Nothing you type is sent to us; the calculators run in your browser.
- 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 trade. Many traders use a fraction of it, such as half Kelly, because full Kelly swings hard when your estimate is off.
- How do I remove the vig from sportsbook odds?
Turn each side’s odds into a chance and divide one side’s chance by the two added together. At −150 and +130 the sides are 60% and 43.5%, 103.5% together, so the fair chance of the favorite is 60 ÷ 103.5 = 58%. The odds converter does it when you enter the other side’s odds.
- Is buying a 95¢ contract worth it?
Only if it wins more than 95% of the time, plus fees. It returns 5.3% if it does, which is a lot a year if it settles soon (about 64% for 30 days) and little if it settles in a year; one loss costs as much as nineteen wins make. The annualized return calculator shows both.
- 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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