Is prediction market arbitrage legal?

Yes. Trading the same contract on two CFTC-regulated platforms is legal for California residents. Both Kalshi and Polymarket allow it.

What's the typical cost of an arbitrage trade?

Round-trip costs run 3-5 cents per contract including trading fees, spreads, and USDC friction. Below that gap, arbitrage isn't profitable.

Why do price gaps exist?

Different user bases, capital inefficiency (most users only fund one platform), different fee structures, settlement differences (USDC vs USD), and occasional resolution rule differences.

What contracts are best for arbitrage?

Major elections, Super Bowl, NBA Finals, World Series, and Fed FOMC. These have identical contract terms on both platforms and deep liquidity.

Is Kalshi. Polymarket arbitrage legal in California?

Yes. Both platforms are CFTC-regulated venues legal in California, so trading opposite sides of the same event across them is legal. What matters is fee-adjusted math, tax reporting, and settlement risk: not legality.

Do you pay taxes on arbitrage profits?

Yes. Every leg of an arb is a taxable event. Net profits from both platforms are ordinary income federally, and California residents owe state income tax on top. Kalshi issues a 1099-MISC above $600; Polymarket requires you to export your on-chain history and file it yourself.

How much capital do you need to arb Kalshi vs Polymarket?

Meaningful arbs typically need $2K: $10K per side to overcome fees, gas, and settlement drift. Below that, per-contract minimums, USDC network gas, and price movement between the two fills usually eat the spread.

Is it worth doing at retail size?

Usually not. Cost structure means you need meaningful price gaps and capital. Where retail can win: persistent gaps on contracts the pros aren't watching.

Do transaction fees eat the profit of a Kalshi-Polymarket arb?

Transaction costs include Kalshi's trading fees and Polymarket's network gas fees for USDC movements. While Polymarket fees are often negligible on the Polygon network, Kalshi charges small transaction fees per contract. Traders must ensure the price spread covers these costs and the slippage from order book depth.

Which platform offers faster settlement for arbitrageurs?

Polymarket often settles immediately following a verified UMA protocol resolution. Kalshi settlements occur after the official source data is verified by their clearinghouse. California traders should account for the capital lock-up period on both platforms when calculating the annual percentage yield of an arbitrage trade.

Are prediction markets legal in California?

Yes. CFTC-regulated event-contract platforms operate under federal commodities law, which preempts state gambling statutes. That makes Kalshi, Polymarket, Sleeper, Chalkboard, Novig, Rebet, and Crypto.com legal for California residents to use today. Even though traditional online sportsbooks remain unavailable in the state.

Who regulates the platforms I am trading on?

The Commodity Futures Trading Commission (CFTC): the same federal agency that regulates futures, options, and swaps. Platforms operate as Designated Contract Markets (DCMs) and must follow rules on disclosures, market integrity, customer protection, and segregation of customer funds.

Do I need to pay California state tax on my winnings?

Yes. Profits are taxable as either short-term capital gains or ordinary income at both the federal and California state level. There is no de minimis exemption. Some Kalshi contracts may qualify for Section 1256 60/40 treatment. Consult a CPA. This is not tax advice.

Is my money protected if a platform fails?

CFTC-regulated platforms are required to keep customer funds segregated from operational capital. That gives meaningful protection in the event of operator bankruptcy, but it is not the same as FDIC insurance. Only fund accounts with money you are prepared to lose.

What disclosures should I read before trading?

Read each platform's contract resolution rules carefully. They vary across venues for the same event. Also review our editorial Disclosure for how we earn revenue from affiliate partnerships and how that affects (and does not affect) our coverage.

What are the age and residency requirements?

You must be 21 or older and a US resident with a valid government ID. KYC verification is mandatory and typically completes in 5-60 minutes.

Guide·7 min read

Arbitrage Between Kalshi and Polymarket: A Realistic Guide

By Catie Di StefanoPublished April 21, 2026Updated September 7, 2026

The same contract trades on both platforms. Sometimes the prices diverge. Here's how prediction market arbitrage actually works, and why it's harder than it looks.

FeaturedPolymarket Kalshi

Some links on this page are affiliate links. We may earn a commission if you sign up, at no cost to you. How we make money.

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Keep the loop going

This month's biggest prediction market movers

A live board of the biggest 30-day probability shifts across every market we track.

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What changed, and when

Dated log of offer, ranking and state-availability changes so you know how current a page is.

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Sources & further reading

Every figure and legal claim on this page traces back to a primary source. These are the ones we checked, open them and verify us.

CFTC: Commodity Futures Trading Commission
The federal regulator that authorizes and supervises every event-contract exchange we cover.
CFTC designated contract markets registry
Official list of registered exchanges, where we verify a platform's DCM status.
Commodity Exchange Act (7 U.S.C. § 1 et seq.)
The federal statute that preempts state gambling law for event contracts.
National Council on Problem Gambling
Free, confidential help and self-assessment tools (1-800-522-4700).

Frequently asked questions

Is prediction market arbitrage legal?: Yes. Trading the same contract on two CFTC-regulated platforms is legal for California residents. Both Kalshi and Polymarket allow it.
What's the typical cost of an arbitrage trade?: Round-trip costs run 3-5 cents per contract including trading fees, spreads, and USDC friction. Below that gap, arbitrage isn't profitable.
Why do price gaps exist?: Different user bases, capital inefficiency (most users only fund one platform), different fee structures, settlement differences (USDC vs USD), and occasional resolution rule differences.
What contracts are best for arbitrage?: Major elections, Super Bowl, NBA Finals, World Series, and Fed FOMC. These have identical contract terms on both platforms and deep liquidity.
Is Kalshi. Polymarket arbitrage legal in California?: Yes. Both platforms are CFTC-regulated venues legal in California, so trading opposite sides of the same event across them is legal. What matters is fee-adjusted math, tax reporting, and settlement risk: not legality.
Do you pay taxes on arbitrage profits?: Yes. Every leg of an arb is a taxable event. Net profits from both platforms are ordinary income federally, and California residents owe state income tax on top. Kalshi issues a 1099-MISC above $600; Polymarket requires you to export your on-chain history and file it yourself.
How much capital do you need to arb Kalshi vs Polymarket?: Meaningful arbs typically need $2K: $10K per side to overcome fees, gas, and settlement drift. Below that, per-contract minimums, USDC network gas, and price movement between the two fills usually eat the spread.
Is it worth doing at retail size?: Usually not. Cost structure means you need meaningful price gaps and capital. Where retail can win: persistent gaps on contracts the pros aren't watching.
Do transaction fees eat the profit of a Kalshi-Polymarket arb?: Transaction costs include Kalshi's trading fees and Polymarket's network gas fees for USDC movements. While Polymarket fees are often negligible on the Polygon network, Kalshi charges small transaction fees per contract. Traders must ensure the price spread covers these costs and the slippage from order book depth.
Which platform offers faster settlement for arbitrageurs?: Polymarket often settles immediately following a verified UMA protocol resolution. Kalshi settlements occur after the official source data is verified by their clearinghouse. California traders should account for the capital lock-up period on both platforms when calculating the annual percentage yield of an arbitrage trade.

Legal & Compliance

Legality, regulation, and your protections

For full guardrails, see our Responsible Trading guide and our editorial Disclosure. This page is informational, not legal or tax advice.

Responsible Trading

Trading safely: the questions that matter

Is trading prediction markets the same as gambling?: No. Prediction markets are CFTC-regulated event contracts, financial derivatives, not casino games. That said, you can still lose every dollar you put in. Treat capital at risk as money you are prepared to lose.
How much should I trade with?: Only with money you can afford to lose without affecting rent, bills, or savings goals. A common rule of thumb: cap total prediction market exposure at 1-5% of your discretionary income.
What are the warning signs of problem trading?: Trading to recover losses, hiding activity from family, borrowing to fund deposits, missing work or sleep, or feeling unable to stop. If any of these apply, step away and call 1-800-GAMBLER.
Where can I get help in California?: Call the California Problem Gambling Helpline at 1-800-GAMBLER (free, confidential, 24/7) or visit ncpgambling.org. Most platforms also offer self-exclusion and deposit limit tools in account settings.
Can I set deposit or loss limits?: Yes. Kalshi, Polymarket, Sleeper, and Chalkboard all offer self-imposed deposit limits, loss limits, and cooling-off periods. Set them when you open the account, not after a bad week.

If you or someone you know needs help, call 1-800-GAMBLER or visit ncpgambling.org.

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California hub

What's live in California this week

Updated weekly: legal markets, top picks, and what to skip.

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Next steps

Top platforms Californians are using:

Polymarket

The world's largest prediction market, now live on iPhone in the US.

21+ Only. Restrictions and eligibility requirements apply. Not available in all jurisdictions. Trading is risky. 100% loss can occur. See polymarket.com/tos for more information. The Polymarket US App serves as an independent software provider and affiliate of Polymarket US and Polymarket Clearing, the CFTC-regulated exchange and clearing organization.

Kalshi

The regulatory leader.

Certain limitations apply. The offer is available to new users only, subject to the terms and conditions at kalshi.com/tc/500. 21+ only. Restrictions and eligibility requirements apply. Event contract trading involves significant risk and is not appropriate for everyone. Please carefully consider if it is appropriate for you in light of your personal financial circumstances. Kalshi products are not available in all jurisdictions. See kalshi.com/regulatory for more information.