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Polymarket Arbitrage Calculator

Free · runs in your browser · live examples updated September 23, 2026

An arbitrage holds both sides of the same event on two exchanges so that one of them always pays $1. It works only when the two prices plus fees cost less than $1. Right now (September 23, 2026) the cheapest pair we track is Which party wins the 2028 presidential election: Republicans on Polymarket at 34.5¢ plus Democrats on Kalshi at 58.5¢ costs 95.6¢ with fees at midpoint prices.

Arbitrage calculator

Price of side A (cents) — e.g. YES on Polymarket Fee on side A Price of side B (cents) — the other outcome, on the other exchange Fee on side B Number of shares / contracts on each side Days until both markets resolve

Total cost incl. fees—

Guaranteed payout—

Profit (or loss)—

Return—

Annualized—

Polymarket taker fee = shares × rate × p × (1 − p); Kalshi general taker fee = 0.07 × contracts × P × (1 − P), rounded up to the next cent. The payout is guaranteed only if both markets resolve on identical rules.

Live cross-exchange pairs

Two-outcome events listed on both Polymarket and Kalshi, with the cheaper way to hold both sides at midpoint prices (real asks are higher). A cost under 100¢ is a gross margin; over 100¢ is a loss.

Event	Polymarket	Kalshi	Fees	Cost	Result per $1	Ends
Which party wins the 2028 presidential election	Republicans 34.5¢	Democrats 58.5¢	2.60¢	95.6¢	+4.4¢	2029-01-21
US recession by the end of 2026	No 91.5¢	Yes 5.5¢	0.75¢	97.8¢	+2.2¢	2026-12-31
Will Anthropic or OpenAI IPO first	OpenAI 5.2¢	Anthropic 92.5¢	0.68¢	98.4¢	+1.6¢	2028-01-01
Which party wins the House in 2026	Republicans 7.5¢	Democrats 91.1¢	0.84¢	99.5¢	+0.5¢	2027-01-05
Which party wins the Senate in 2026	Republicans 34.5¢	Democrats 64.5¢	2.51¢	101.5¢	-1.5¢	2027-01-05

Why most arbitrage is not free money

⚠️ Access. Kalshi serves US residents; polymarket.com is close-only for US users (details). Few traders can legally use both.
⚠️ Rules. The two markets must resolve on the same facts, sources and deadline. Wording differences can make both sides lose.
⚠️ Prices. Midpoints are not fills: you buy at the ask, and large orders move the price.
⚠️ Time. Money is locked until both markets settle — a 3% margin over two years is about 1.5% a year.

See the full side-by-side on Polymarket vs Kalshi odds today.

Frequently asked questions

Can you arbitrage Polymarket and Kalshi?

Only when the two prices plus fees add up to less than $1 for the same outcome set, the rules match, and you can legally use both platforms — which is rare, because Kalshi serves US residents and polymarket.com is close-only in the US.

How are fees included in the calculation?

Polymarket charges takers shares × rate × p × (1 − p) with a category rate; Kalshi's general taker fee is 0.07 × contracts × P × (1 − P), rounded up to the next cent. The calculator adds both to the cost.

What is a good arbitrage margin?

Anything above zero after fees is a gross profit, but compare it with the time until settlement: annualize it, and weigh the rule and access risks before trading.

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All tools · Polymarket fees · Polymarket vs Kalshi odds · Polymarket odds today. Polymarket View is independent and not affiliated with Polymarket, Kalshi or any sportsbook. Educational math, not financial or betting advice.