Prediction market tools
Two calculators, both running in your browser. The odds converter turns American, decimal or fractional odds into the probability a contract price already states, and strips a sportsbook's vig. The payout calculator shows what a Polymarket, Polymarket US or Kalshi position pays, what the fee costs and the probability it needs to break even.
Odds converter
American, decimal, fractional and cent prices, the payout on any stake, and a no-vig calculator for a sportsbook's two sides.
Example: a contract at 62¢ is -163 American, 1.61 decimal, 19/31 fractional. A −110 / −110 line adds up to 104.8% and keeps 4.5% of every dollar staked.
Payout calculator for Polymarket, Polymarket US and Kalshi
Stake and price in. Contracts, fee, payout, break-even and expected profit out, with Polymarket, Polymarket US and Kalshi fees and their rounding.
Example: $100 of Yes at 62¢ on Kalshi buys 161.29 contracts, pays $161.29 if right after a $2.66 fee, and breaks even at 63.6%.
What each tool answers
Odds converter
- What a sportsbook's +150 means as a probability, and what the same chance costs as a contract.
- What a −110 / −110 line really implies once the book's margin is taken out.
- How a 62¢ contract reads in American, decimal and fractional odds, so a market price and a sportsbook line can be set against each other.
Payout calculator
- How many contracts a stake buys at a price, and what they pay if the answer is yes.
- The exact fee on each venue, from its published schedule and with its own rounding: at 50¢, $100 costs $2.00 on Polymarket (international book), $3.48 on Polymarket US, $3.50 on Kalshi.
- The probability the trade needs to break even, and your expected profit at your own probability.
Cents to odds, and what $100 pays
| Price | Chance | American | Decimal | Fractional | Polymarket US pays | Kalshi pays |
|---|---|---|---|---|---|---|
| 10¢ | 10% | +900 | 10.00 | 9/1 | $1,000.00 | $1,000.00 |
| 25¢ | 25% | +300 | 4.00 | 3/1 | $400.00 | $400.00 |
| 40¢ | 40% | +150 | 2.50 | 3/2 | $250.00 | $250.00 |
| 50¢ | 50% | +100 | 2.00 | 1/1 | $200.00 | $200.00 |
| 62¢ | 62% | -163 | 1.61 | 19/31 | $161.29 | $161.29 |
| 75¢ | 75% | -300 | 1.33 | 1/3 | $133.33 | $133.33 |
| 90¢ | 90% | -900 | 1.11 | 1/9 | $111.11 | $111.11 |
Payouts are what $100 of Yes returns if the answer is yes, after each venue's taker fee at the standard rate, from the same code the calculators run. Polymarket's international book pays $161.29 on $100 at 62¢ in a politics market.
The pages the tools draw on
Fees by venue
What every venue charges, and the formula behind the calculator's fee line.
Implied probability
Why a price is a probability, and how each odds format encodes it.
What prediction markets are
The $1-or-$0 contract the calculators assume.
Live odds
Every market priced now, to try a real price in the calculator.
Kalshi's fee models
The per-series multipliers behind the Kalshi tab.
Polymarket's fee schedule
The category rates behind the Polymarket tab.
Common questions
Which tool do I need?
The odds converter when you have a sportsbook line or a probability and want the other. The payout calculator when you have a stake and a contract price and want the fee, the payout and the break-even.
Where do the fee rates come from?
From each venue’s published schedule, recorded in the venue registry and linked on the fees page. The calculators and every worked number on these pages run the same code, so they cannot disagree.
Why is a contract price already a probability?
A Yes contract pays $1 if the answer is yes and nothing if not, so a price of 62¢ is the market saying 62%. Sportsbook odds encode the same chance plus the book’s margin, which the converter strips out.
Do the tools send my numbers anywhere?
No. Both run entirely in your browser; nothing you type leaves the page.