"How to convert Polymarket prices to odds (decimal, American, fractional)"
Polymarket doesn't show odds. Every outcome has a price between 1 and 99 cents instead. If you come from sportsbooks, the first thing you want is to turn that price into odds. It's one step.
The formula
Decimal odds = 1 / price.
A price in cents is a fraction of a dollar: 40¢ = 0.40, so decimal odds = 1 / 0.40 = 2.50. You pay 40 cents for a share that pays $1 if the outcome happens — exactly like a 0.40 stake at 2.50.
Cheat sheet: price → decimal odds
- 10¢ → 10.00
- 20¢ → 5.00
- 25¢ → 4.00
- 33¢ → 3.03
- 40¢ → 2.50
- 50¢ → 2.00
- 60¢ → 1.67
- 70¢ → 1.43
- 80¢ → 1.25
- 90¢ → 1.11
The price is also a probability
A 40-cent price means the market gives the outcome roughly a 40% chance. That's cleaner than a sportsbook line, where you have to strip out the vig to see what the book really believes.
American odds
Price below 50¢: +(100 / price − 100). 40¢ → +150. Price above 50¢: −(price / (1 − price) × 100). 60¢ → −150.
Fractional odds
Fractional = (1 − price) / price. 40¢ → 0.60 / 0.40 = 3/2. 25¢ → 3/1.
Going the other way
Price = 1 / decimal odds. A sportsbook offers −125 (1.80)? That's 1 / 1.80 ≈ 56 cents. If Polymarket has the same outcome at 52 cents, Polymarket is the better price (1.92).
Things that change your real odds
- The price you see is often the last trade or the midpoint. You buy at the ask, usually about a cent higher.
- Some markets charge a fee, which trims your effective odds a little.
- Big orders walk the order book: buy a lot and your average price gets worse.
PrognosX shows every Polymarket price as odds, and you can pick decimal, American, fractional or cents in your profile. See where the big money is going in the whale feed.