How Arbitrage Works in Prediction Markets: Kalshi, Polymarket, and Cross-Platform Opportunities
When the same event is priced differently on two prediction markets, a gap appears. If you can buy YES on one platform and NO on the other for a combined cost of less than $1, the difference is a guaranteed profit regardless of the outcome. That is arbitrage — and in prediction markets, it happens more often than you might expect.
What Is Prediction Market Arbitrage?
Arbitrage is the practice of exploiting price differences for the same event across different platforms. In prediction markets, it works like this:
Suppose Kalshi prices “Will the Fed cut rates in June?” at 62¢ YES, while Polymarket prices the same event at 35¢ NO. You are paying 62¢ + 35¢ = 97¢ to cover both outcomes. One side will pay $1. Your guaranteed profit is 3¢ per contract, regardless of what the Fed does.
The concept is simple. The execution is where it gets complicated.
Why Do Price Differences Exist?
Prediction markets are not perfectly efficient. Prices can diverge across platforms for several reasons:
Different user bases
Kalshi's user base skews toward US retail traders in a regulated environment. Polymarket's international user base includes crypto-native participants with different risk preferences and information sources.
Liquidity varies by platform and market
A headline political market might be deep on Polymarket but thin on Kalshi, or vice versa. Thin order books mean prices can drift further from consensus.
Fee structures differ
Kalshi's formula-based fees, Polymarket's variable fee model, and PredictIt's 10% profit plus 5% withdrawal fees all create different effective costs. A price that looks like an arbitrage opportunity before fees may not be one after fees.
Settlement and resolution differences matter
Even when two platforms appear to list the same event, the exact resolution criteria can differ. If the resolution criteria are not truly identical, it is not a true arbitrage — it is two correlated but distinct bets.
How to Identify Arbitrage Opportunities
The basic math is straightforward. Take the lowest available YES price across all platforms. Take the lowest available NO price across all platforms. If the two prices sum to less than $1 (before fees), a theoretical arbitrage exists.
Platform A: YES at 58¢
Platform B: NO at 39¢
Total cost: 97¢
Theoretical profit: 3¢ per contract pair
But before you execute, you need to subtract fees from both sides. Kalshi’s fee on a 58¢ contract is roughly 1.7¢. Polymarket may or may not charge a fee depending on the market category. If total fees exceed your 3¢ gross margin, the arbitrage disappears. To check whether the vig built into any set of prices leaves room for an edge, use the Vig Calculator. To evaluate expected value on a single-platform trade, use the EV Calculator.
Cross-Platform Arbitrage: Kalshi vs Polymarket
Kalshi and Polymarket are the two most commonly compared platforms for arbitrage because they have the most overlapping markets. Both list contracts on politics, economics, sports, and other major event categories. However, executing cross-platform arbitrage between them involves real friction:
Capital is locked on both platforms simultaneously. You need funded accounts on both Kalshi and Polymarket, and your capital is tied up until the event resolves — which could be days, weeks, or months.
US access differs. Kalshi is available to US residents through its established CFTC-regulated setup. Polymarket’s US access runs through a separate entity that is still being rolled out. Verify your eligibility on both platforms before assuming you can execute cross-platform trades. For a full comparison, see Kalshi vs Polymarket.
Resolution risk is real. Even when two markets appear identical, subtle differences in resolution criteria can mean one side pays out and the other does not. Always read the fine print on both platforms before treating two contracts as interchangeable.
Opportunities are episodic. Prediction market arbitrage is not a steady income stream. Price gaps appear and close quickly, often within minutes. Sustained arbitrage requires monitoring tools, fast execution, and enough capital deployed across platforms to make small per-contract margins meaningful.
Does Arbitrage Actually Work in Practice?
Sometimes, but not as often or as easily as the math suggests:
Thin margins get thinner after fees. A 3¢ theoretical spread becomes 0–1¢ after platform fees on both legs. Many apparent opportunities are not profitable net of friction.
Speed matters. Other traders — including automated systems — are watching the same price gaps. By the time you spot an opportunity and place orders on two platforms manually, the gap may have closed.
Capital efficiency is poor. Locking up money on two platforms for weeks to earn 2–3% is a low return on capital, especially when that capital could be deployed in higher-conviction single-platform trades.
Slippage on thin markets can eliminate your edge. The quoted price and the price you actually get filled at can differ, especially on larger orders. For more on how slippage works on Kalshi specifically, see What Is Kalshi?
That said, genuine arbitrage opportunities do appear — particularly around breaking news, when one platform’s order book adjusts faster than another’s, or in niche markets where fewer participants are monitoring prices.
The Role of Fees in Arbitrage
Fees are the single biggest factor that turns theoretical arbitrage into a losing trade. Consider this example:
Platform A: YES at 55¢ (fee: ~1.7¢)
Platform B: NO at 42¢ (fee: ~1.7¢)
Gross spread: 3¢
Total fees: ~3.4¢
Net result: −0.4¢ per contract
A trade that looked profitable on paper costs you money after fees. This is why understanding each platform’s fee structure in detail is essential before attempting any arbitrage strategy. See Prediction Market Fees Compared for a side-by-side breakdown.
What About PredictIt?
PredictIt’s fee structure — 10% on profits plus 5% on withdrawals — makes it particularly difficult to include in arbitrage strategies. The profit fee alone can consume most or all of a thin arbitrage margin. In practice, PredictIt is rarely the right venue for cross-platform arbitrage.
Frequently Asked Questions
Common questions about prediction market arbitrage.
Can you arbitrage between Kalshi and Polymarket?
In theory, yes — when the same event is priced differently on both platforms, an arbitrage opportunity can exist. In practice, fees, different resolution criteria, capital lockup, and US access limitations make execution more complicated than the math alone suggests. Always verify that the contracts on both platforms resolve under truly identical criteria.
Is prediction market arbitrage risk-free?
Not entirely. True arbitrage — where you hold both sides of an identical binary outcome — eliminates market risk. But execution risk (slippage, partial fills), resolution risk (different settlement criteria), and fee risk (costs exceeding the spread) all remain. "Risk-free" is a theoretical concept that rarely survives contact with real-world trading friction.
How much money do you need for prediction market arbitrage?
There is no minimum, but the math favors larger positions. A 2¢ per-contract profit on 10 contracts is 20¢. On 1,000 contracts, it is $20. Since you need funded accounts on multiple platforms with capital locked until resolution, meaningful arbitrage typically requires several hundred dollars deployed across platforms at minimum.
Is arbitrage legal on prediction markets?
Yes. Arbitrage is a standard trading practice and is not prohibited by any major prediction market platform. In traditional financial markets, arbitrage is considered a healthy market function that helps keep prices aligned across venues.
Educational content only. This article is for informational purposes and does not constitute financial, legal, or tax advice. Prediction market trading carries significant risk. Past results, fee estimates, and legal summaries may not reflect current conditions. Always consult a qualified professional before making financial decisions.