Polymarket Odds Explained: Prices, Probability and Payouts

The price is a probability

A share pays $1 if the outcome happens. Its price, between 0 and 1, is therefore the probability the market assigns to that outcome: $0.25 = 25%, $0.80 = 80%.

Converting a price into odds

Decimal odds are simply 1 / price. American odds follow from them: below 0.50 they are positive (+100 × (1 − price) / price), above 0.50 they are negative (−100 × price / (1 − price)).

Share price	Probability	Decimal odds (before fees)	American odds	$10 staked returns
$0.20	20%	5.00	+400	$50
$0.50	50%	2.00	+100	$20
$0.80	80%	1.25	−400	$12.50

Your real payout, fees included

Fees reduce the number of shares you receive. On a sports market, Polymarket charges about 5% × (1 − price) of the amount; a copy bot adds its own fee (2% on PolyCopy). The real odds become:

real odds ≈ (1 − fees) / price

Example at 0.50: 0.98 × (1 − 0.05 × 0.5) / 0.50 ≈ 1.91 instead of 2.00. On a market without Polymarket fees, you stay at 0.98 / 0.50 = 1.96.

Displayed price, buy price, sell price

The displayed price is often the last trade or the midpoint. To buy right away you pay the best ask (slightly higher); to sell right away you get the best bid (slightly lower). On an active market the gap is one cent; on a thin market it can exceed 5%.

Better than a sportsbook?

Not always. A sportsbook builds a margin into every outcome; Polymarket doesn't, but it has its fees. In our October 2026 comparisons on football, Polymarket often paid better on underdogs, about the same on favourites, and worse on some draws. Always compare outcome by outcome, fees included. The other differences (margin, reselling, legality) are in our Polymarket vs sportsbook comparison.