When the same event trades at different prices on Kalshi and Polymarket, you can sometimes buy both sides for less than $1 combined and lock in a profit no matter the outcome. This calculator checks whether a given pair of prices is a real arbitrage once fees are considered.
Enter the two prices below. Remember that thin liquidity and fees often erase apparent arbs, so always sanity-check against the real order books.
COMBINED COST
93¢
per Yes + No pair
TOTAL OUTLAY
$96.49
incl $3.49 fees
LOCKED PROFIT
$3.51
ROI
3.6%
guaranteed either way
Yes and No together pay exactly $1 at settlement, so a combined cost under $1 is a theoretical arbitrage. Fees and thin liquidity at the quoted prices often erase it, so always verify against the live order books before trading.
How the arb works
In a single binary event, Yes and No together always pay exactly $1 at settlement. So if you buy Yes on one platform and No on another for a combined total under $1, the difference is locked-in profit regardless of how the event resolves.
Why it is rarely free money
Two frictions usually close the gap: fees on each leg, and limited liquidity at the quoted prices. A combined cost of 98 cents looks like a 2 cent edge, but taker fees on both sides and slippage on a thin book can wipe it out. Treat any apparent arb with suspicion and compute the all-in cost.
FAQ
What is prediction market arbitrage?
Buying both sides of the same event across platforms (Yes on one, No on the other) for under $1 combined, locking in a guaranteed profit regardless of outcome.
Is Kalshi-Polymarket arbitrage risk-free?
Rarely. The theoretical profit is often erased by fees on each leg and by limited liquidity at the quoted prices. Always compute the all-in cost and check the real order books.
How do I find arbitrage opportunities?
Compare the same event's prices across platforms and look for a combined Yes-plus-No cost under $1. This calculator tells you the profit and ROI once you enter the two prices.
Stop calculating one trade at a time
ContractTax does this across your whole Kalshi history: real P&L, a Sharp Score that rates your edge, and your tax numbers under every treatment.
These tools are for education and estimation only, not financial or tax advice. Fee estimates use Kalshi’s standard formula and may differ from your actual fees.