How to read Kalshi odds and Polymarket prices: implied probability, American and decimal odds
A 40¢ price means a 40% chance. How to turn Kalshi and Polymarket prices into American, decimal and fractional odds, why prices add up to more than 100%, and how fees change your break-even.
Prediction market odds are easier to read than sportsbook odds: the price is the probability. A contract trading at 40¢ on Kalshi, or a share at 40¢ on Polymarket, means the market gives that outcome about a 40% chance, because it pays $1 if it happens and $0 if it does not.
This guide shows how to read a price, convert it into the odds formats sportsbooks use, and work out what you actually need to win after costs.
How to understand prediction market odds
- Price = implied probability. 25¢ ≈ 25%. 90¢ ≈ 90%.
- Payout = $1 per contract if you are right. Your profit is $1 minus the price you paid, minus fees.
- "Yes" and "No" are two sides of one market. If "Yes" is 40¢, "No" is about 60¢. Buying "No" at 60¢ is the same bet as selling "Yes" at 40¢.
Example: you buy 50 contracts at 40¢ for $20. If the outcome happens you receive $50, a $30 profit before fees. If not, you lose the $20.
Converting prices to sportsbook odds
| Price / chance | Decimal | American | Fractional |
|---|---|---|---|
| 5¢ / 5% | 20.0 | +1900 | 19/1 |
| 10¢ / 10% | 10.0 | +900 | 9/1 |
| 20¢ / 20% | 5.0 | +400 | 4/1 |
| 25¢ / 25% | 4.0 | +300 | 3/1 |
| 40¢ / 40% | 2.5 | +150 | 3/2 |
| 50¢ / 50% | 2.0 | +100 (even) | 1/1 |
| 60¢ / 60% | 1.67 | −150 | 2/3 |
| 75¢ / 75% | 1.33 | −300 | 1/3 |
| 90¢ / 90% | 1.11 | −900 | 1/9 |
The formulas, with p as the price in dollars:
- Decimal odds = 1 ÷ p.
- American odds, if p is below 0.5: +100 × (1 − p) ÷ p. If p is 0.5 or more: −100 × p ÷ (1 − p).
- Back from American: +300 → 100 ÷ (300 + 100) = 25%. −150 → 150 ÷ (150 + 100) = 60%.
Real examples from October 2026: the Brewers at 65% to win the World Series is about −188, and the 49ers at about 14% to win the Super Bowl is about +620. See World Series odds and Super Bowl odds.
Kalshi odds: what the number on the screen means
Kalshi shows each outcome's chance next to buy prices for "Yes" and "No". The number to focus on is the price you would pay, the ask, because that is your real cost. On busy markets the gap between bid and ask (the spread) is a cent or two; on thin ones it can be much wider. How Kalshi contracts and orders work: how does Kalshi work.
Polymarket prices: midpoint or last trade
Polymarket shows the midpoint between the best bid and the best ask as the market's probability. When the spread is wide (more than 10¢), it shows the last traded price instead. Either way, the price you pay when you buy at market is the ask, which can be higher than the headline number. The details: what slippage means.
Why the prices add up to more than 100%
In a market with many outcomes, such as a championship, the "Yes" prices often add up to slightly more than 100%. On a championship market the prices you can buy at typically total a few points over 100%. The extra is the market's version of a sportsbook's margin: it comes from the spread, because each price you can buy at is a little above the fair value.
To get a fair probability, divide each price by the total. If a team is 22¢ and all prices sum to $1.04, its fair chance is about 21.2%. Our Compare page and election hub normalise prices this way.
How fees change your break-even
Fees mean you need to be right a bit more often than the price suggests. On Kalshi a taker pays 7% × p × (1 − p) per contract:
- Buy at 40¢: the fee is about 1.7¢, so your all-in cost is about 41.7¢ and you need the outcome to happen more than 41.7% of the time to profit.
- Buy at 90¢: the fee is about 0.6¢, so you need more than about 90.6%.
Polymarket's global site uses the same shape with a rate per category, and some markets are free. Worked examples in Polymarket fees vs Kalshi fees.
Compared with a sportsbook
A typical sportsbook line of −110 on both sides implies 52.4% + 52.4% = 104.8%, a margin of about 4.5% built into the odds. On a liquid prediction market the total cost is usually the spread plus the fee, often less than that, and you can sell before the event ends. On thin markets it can be more.
Are prediction market odds accurate?
Over many markets, prices have tracked real-world frequencies reasonably well: things priced at 70% tend to happen about 70% of the time. But any single price can be wrong, especially on thin markets or right after news. The case for and against: how do prediction markets work.
Prediction market odds: frequently asked questions
What does 70% mean on Kalshi?
That contracts trade around 70¢, so the market gives the outcome about a 70% chance. It pays $1 per contract if it happens.
How do I convert Kalshi odds to American odds?
Below 50¢: +100 × (1 − p) ÷ p. At or above 50¢: −100 × p ÷ (1 − p). So 25¢ is +300 and 75¢ is −300.
Are Polymarket odds the same as probability?
They are the market's implied probability, not a guarantee. Read them as the crowd's current estimate.
Why are Kalshi and Polymarket odds different for the same event?
They are separate markets with different traders and fees. Gaps of a few points are common: see prediction market arbitrage.
