Comparator
Kalshi vs Polymarket Arb Scanner
Daily scan of arbitrage candidates across Kalshi + Polymarket. Paired contracts, fees + slippage overlay, resolution risk notes.
Runs in your browser. Nothing you enter is uploaded, and no account or API key is needed.
Check a pair of quotes
Basis points of the $1 payout, your estimate for both venues.
Number of $1 YES + NO pairs to buy.
Buy YES on Kalshi + NO on Polymarket
Gross edge 300 bps, net 150 bps after costs. Costs $970.00 for $1,000 of payout; expected P&L $15.00 (1.55% on cash spent) if both legs fill and both venues resolve the same way.
How to use it
- Read the YES and NO asks for the same event on Kalshi and on Polymarket and enter them in the pair checker, in cents.
- Set your fee and slippage assumptions (basis points of the $1 payout) and the payout notional you want to buy.
- Read the direction (which venue's YES to pair with the other's NO), the gross and net edge, the cash required and the expected P&L.
- Before trading, compare both contracts' resolution rules and check that the books are deep enough to fill your size at the quoted asks.
- The leaderboard below the checker runs on synthetic demo pairs to show the math; it is not live data.
Questions people ask
What's Kalshi-Polymarket arbitrage?
When the same event trades on both Kalshi (a CFTC-regulated US exchange) and Polymarket, buying YES on one venue and NO on the other pays exactly $1 whichever way it resolves. If the two asks add up to less than $1 (for example YES at 54¢ on Kalshi plus NO at 43¢ on Polymarket = 97¢), the 3¢ difference is a locked-in gross edge of 300 basis points, before fees, slippage and the time your cash is tied up. The calculator checks both directions and returns the better one.
Why doesn't the arbitrage close instantly?
Because moving money and accounts between the venues is slow and the two user bases differ: Kalshi needs US KYC and dollar funding, Polymarket a crypto wallet and USDC. Books on both sides can be thin, so the quoted ask may only cover a small size. The tool does not size the trade to available depth; enter a payout notional you can actually fill and a slippage assumption to match.
What fees does the calculator include?
The ones you enter: a combined fee and a slippage assumption, both in basis points of the $1 payout. It does not apply either venue's fee schedule automatically, and it ignores funding, bridging or withdrawal costs and the cost of capital locked until resolution, so set the fee input from the venues' current fee pages for the contracts you trade.
Are the events actually equivalent?
You have to check. The calculator assumes both contracts resolve on exactly the same outcome; it does not compare resolution rules. Small differences in source, threshold or deadline (for example 'by July 31' against 'in July') can make one leg win and the other lose, turning an apparent arbitrage into a loss. The demo pairs list resolution risks to show what to look for.
Should I actually trade these?
Not on this page's demo data: the leaderboard is three synthetic pairs, not live quotes. For real quotes the calculator gives the arithmetic edge only. Real-world arbitrage also needs funded accounts on both venues, fills at the quoted asks, identical resolution, and enough edge to beat the return your capital would earn while it waits for settlement.
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Use it from code
The same calculation as a JavaScript module you can import. It runs where you import it, with no request, key or rate limit.
import { compute } from "https://aifinhub.io/engines/kalshi-poly-arb.js";