Beginner guide
How prediction market odds work
On Kalshi and Polymarket, the price is the odds. A contract that costs 62¢ pays $1 if it happens, so the market is saying there's about a 62% chance. Here's how that works, what you can win or lose, and how it compares with sportsbook odds.
The price is the chance
Every contract pays $1 if it happens and $0 if it doesn't. So the price, in cents, is the market's estimate of the chance:
| YES price | Market's chance | Cost of 10 | Paid if YES |
|---|---|---|---|
| 10¢ | about 10% | $1.00 | $10.00 |
| 25¢ | about 25% | $2.50 | $10.00 |
| 50¢ | about 50% | $5.00 | $10.00 |
| 62¢ | about 62% | $6.20 | $10.00 |
| 90¢ | about 90% | $9.00 | $10.00 |
Before fees. Fees are covered below.
YES and NO are two sides of the same question, so their prices add up to about $1. If YES is 62¢, NO is about 38¢.
A worked example
You buy 10 YES at 62¢. That costs $6.20.
- If it happens: you get $10.00 back, a $3.80 profit before fees.
- If it doesn't: you lose the $6.20.
- Before it settles: you can sell at whatever the market pays at that moment, for a profit or a loss.
Buy price and sell price
Each market has a price to buy (the ask) and a lower price to sell (the bid). If YES shows 62¢ to buy and 60¢ to sell, buying and selling straight away loses 2¢ a contract. The gap is usually small on busy markets and wide on quiet ones.
Converting to sportsbook odds
If you're used to sportsbooks, these are the same numbers written differently:
| Price | Chance | Decimal | American |
|---|---|---|---|
| 20¢ | 20% | 5.00 | +400 |
| 25¢ | 25% | 4.00 | +300 |
| 40¢ | 40% | 2.50 | +150 |
| 50¢ | 50% | 2.00 | +100 |
| 62¢ | 62% | 1.61 | −163 |
| 75¢ | 75% | 1.33 | −300 |
Decimal = 1 ÷ price. American, under 50¢: +(1 − price) ÷ price × 100. Over 50¢: −price ÷ (1 − price) × 100. The odds converter does it for any number.
Fees change the math
Most apps charge a fee when you buy. On Kalshi the taker fee is 0.07 × contracts × price × (1 − price), rounded up to the cent. For 10 contracts at 62¢ that's $0.17, so the trade costs $6.37 and the profit if it wins is $3.63.
That also moves your break-even: at $6.37 for a $10 payout, the event has to happen about 63.7% of the time for you to come out even over many bets, not 62%. Fees differ by app. See fees compared.
Is the price the real chance?
It's the market's best guess, set by what people will pay. It's often good, but it's not a fact. Prices can be off when a market is quiet, when news is breaking, or when lots of money is on one side for reasons other than the odds.
That's why the same event can have different prices on two apps at the same moment. When the gap is bigger than the fees on both sides, buying YES on one and NO on the other can pay whoever wins. That's what ArbTrader scans for, along with the biggest bets as they land and an AI research read on any market.
Not financial advice. ArbTrader isn't affiliated with Kalshi or Polymarket.
Common questions
What does 62 cents mean on Kalshi or Polymarket?
The contract pays $1 if the event happens, so a 62¢ price means the market puts the chance at about 62%. Buying one costs 62¢ plus any fee, and pays $1 if you're right.
How much do you win on a prediction market?
Each contract pays $1 if it happens. Your profit is $1 minus what you paid and the fee. 10 contracts bought at 62¢ pay $10, a $3.80 profit before fees.
How do I convert a prediction market price to American odds?
Under 50¢: (1 − price) ÷ price × 100, with a plus sign. Over 50¢: price ÷ (1 − price) × 100, with a minus sign. 25¢ is +300 and 75¢ is −300.
Why do Kalshi and Polymarket show different odds?
They're separate markets with different traders, fees and rules, so prices drift apart. Usually the gap is smaller than the fees. Sometimes it isn't.
See the odds on Kalshi and Polymarket side by side, free.
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