Prediction Market Odds Converter
Convert between Polymarket, Kalshi, American, decimal and fractional odds with implied probability
Percent (0.1-99.9)
Polymarket prob = cents / 100
Kalshi prob = price
American (+) prob = 100 / (odds + 100)
American (-) prob = |odds| / (|odds| + 100)
Decimal prob = 1 / decimal
Fractional prob = b / (a + b)
At 65.0% implied probability, this outcome is slightly more likely than not — a coin flip leaning in its favor.
What Are Prediction Markets?
Prediction markets are platforms where you can trade on the outcome of real-world events. Instead of betting on sports or games, you trade contracts on questions like "Will X happen by Y date?" Each contract pays out $1 if the event occurs and $0 if it doesn't. The current trading price reflects the crowd's consensus probability of the event happening. Platforms like Polymarket and Kalshi have made prediction markets accessible to mainstream users, covering politics, economics, crypto, sports, and more.
Understanding Polymarket & Kalshi Pricing
On Polymarket, contracts trade in cents from 0 to 99. A contract at 65 cents means the market believes there's a 65% chance the event will happen. If you buy YES at 65 cents and the event occurs, you receive $1.00 — a profit of 35 cents per contract. On Kalshi, the pricing works identically but is expressed as a dollar price from $0.01 to $0.99. A contract at $0.65 implies the same 65% probability. Both platforms use the contract price as a direct proxy for implied probability, making them the most intuitive odds format for newcomers.
Implied Probability Explained
Implied probability is the percentage chance of an outcome occurring as derived from the odds. It is the canonical measure that all other odds formats are converted to and from. A 50% implied probability means the event is a coin flip. A 75% probability means the market expects the event to happen three out of four times. Understanding implied probability is crucial because it allows you to compare odds across different formats and platforms on equal footing. If your own analysis suggests a higher probability than what the market implies, you may have found a value bet.
American vs Decimal vs Fractional Odds
American odds are the standard in US sportsbooks. Positive odds (e.g. +200) indicate how much profit you'd make on a $100 stake. Negative odds (e.g. -150) indicate how much you need to stake to profit $100.
Decimal odds (e.g. 2.50) are popular in Europe and show the total return per $1 staked, including your original stake. A decimal of 2.50 means you receive $2.50 back for every $1 bet (including the $1 stake), for a net profit of $1.50.
Fractional odds (e.g. 3/2) are the UK standard. They represent the ratio of profit to stake. At 3/2, you profit $3 for every $2 staked. Fractional odds of 1/1 (evens) correspond to a 50% probability.
Why Odds Matter for Finding Value
The key to profitable prediction market trading is finding discrepancies between the market's implied probability and your own assessed probability. If a contract trades at 40 cents (40% implied) but you believe the true probability is 60%, that contract is underpriced and represents a value opportunity. Converting between odds formats fluently allows you to quickly spot these discrepancies whether you're comparing Polymarket prices with sportsbook lines or evaluating the same event across different platforms. Always remember: markets are not always right, but they aggregate a lot of information. Your edge comes from having better information or analysis than the crowd.