Prediction Market Prices vs Sportsbook Odds: How to Compare Them
Sportsbooks quote American odds such as -150 or +130. Prediction markets such as Kalshi and Polymarket quote something different: a price between 0 and 100 cents (or 0 and 1 dollar) for a contract that pays out if an outcome happens. To compare the two, you need to convert one into the other.
How a prediction market price works
On a prediction market, a "Yes" contract pays 1 dollar if the event happens and nothing if it does not. If a contract trades at 60 cents, the market is implying about a 60% chance, because paying 60 cents for a 1-dollar payout only breaks even if the event happens 60% of the time.
Converting a price to American odds
Take the price as a probability p (for example 0.60).
- If p is 50% or higher, the American odds are negative: odds = -(p ÷ (1 - p)) × 100. At 60%, that is -(0.60 ÷ 0.40) × 100 = -150.
- If p is below 50%, the American odds are positive: odds = ((1 - p) ÷ p) × 100. At 40%, that is (0.60 ÷ 0.40) × 100 = +150.
So a 60-cent Yes contract and a -150 sportsbook price describe the same implied probability, and so do a 40-cent contract and +150.
Each side has its own price
A prediction market has a buy price for each side, and the two do not always add up to exactly 100 cents. The "No" side is a separate contract you can buy. This is why ArchivePicks shows each side at the price someone could actually buy it at, rather than assuming one side is simply 100 minus the other. See the methodology for how this is handled.
Why compare them at all
Sportsbooks build a margin into their prices: a -110 / -110 market adds up to about 104.8% implied probability. A prediction market's prices on the two sides usually sit closer to 100% combined, though trading costs and spreads still apply and vary by market. Putting the converted prices next to each other makes it easy to see where the sources agree and where one is out of line.
Cautions
- Liquidity. A thinly traded contract can have a wide gap between what buyers pay and what sellers ask, so its displayed price may not be one you can actually trade at.
- Timing. Prices move. A price on the board can be slightly out of date and may already have changed at the source.
- Rules differ. Sportsbooks and prediction markets can define the same event slightly differently, for example when a game is postponed or a player does not play. Read the rules of the venue you use.
ArchivePicks shows prices from several sources side by side for NFL games. It does not take bets, does not hold money and does not tell you which side to take.