Prediction market arbitrage calculator
Enter the YES price on one venue and the NO price on another. See what the pair costs after taker fees, and whether it locks in a profit.
On the odds board a NO price is 100¢ minus the other side's YES bid. Fees assume a taker fill at the price you enter.
FAQ
How does prediction market arbitrage work?
You buy YES on one venue and NO on another for the same outcome. One of the two contracts pays $1 whatever happens, so if both together cost less than $1 after fees, the difference is locked in. In practice the gap is usually smaller than the two taker fees.
How are the fees calculated?
Each venue charges rate × contracts × price × (1 − price) on a taker fill: 0.07 on Kalshi, 0.0695 on Polymarket US and 0.05 on Polymarket sports markets. The calculator assumes you buy at the ask. Kalshi rounds its fee up to the next cent per order, so very small orders cost slightly more.
What else can go wrong?
The two venues may word the question differently and settle it differently, prices can move before both orders fill, and withdrawals take time and sometimes cost money. Read both venues’ resolution rules first. Polymarket’s international site doesn’t accept US users.