Kalshi Arbitrage: How to Find Real Cross-Venue Price Gaps

Kalshi arbitrage is potential profit from a price gap between a Kalshi event contract and a matching market on another venue, often Polymarket. The usual setup is buying YES where it is cheap and buying NO where the opposite side is cheap, with the combined executable cost below the payout. A visible spread is only a lead, not a guaranteed trade.

Before acting, verify: Use the Predicts.Guru Arbitrage Scanner to find cross-venue leads, then check both market pages manually.

Kalshi arbitrage looks simple because binary markets have clean prices. If one market shows YES at 44 cents and another venue lets you buy the opposite side at 53 cents, the math appears to leave 3 cents of spread. That is only the starting point.

The real question is whether both legs can be entered at those prices, in enough size, under matching settlement criteria. Manually checking Kalshi, Polymarket, and other prediction markets is slow. It is also easy to mistake a headline price for an executable price.

A real cross venue arbitrage candidate needs four things at once: Kalshi's own help materials tell traders to read each market's rules before trading because market-specific rules define the criteria, verification source, and procedures for resolution. Polymarket's docs make the same point in a different way: the market title describes the question, but the resolution rules define how it resolves.

That is where many Kalshi price differences break. A spread can be real as a screen result and still fail as a trade.

Real Kalshi arbitrage exists when two positions create a defined payout profile across the same real-world event, and the total executable cost is less than the payout after costs. A practical rule of thumb: Executable YES cost + executable NO cost + fees + expected slippage must be below the guaranteed payout.

In most simple binary event markets, that payout is $1.00 per complete YES/NO hedge if the markets truly match. If the all-in cost is $0.98, there may be a 2 cent gross edge. If the all-in cost is $1.01, there is no arbitrage even if the headline prices looked attractive.

Binary prediction markets usually price outcomes between $0.00 and $1.00. Kalshi explains prices as market-assigned probabilities, where a 70 cent YES contract implies roughly a 70% market probability and a complementary NO side near 30 cents. Polymarket's prices and order book documentation describes a similar probability interpretation for shares.

A hypothetical YES NO prediction market arbitrage example: This example is not live pricing. It is only the arithmetic.

Now pressure-test it: A 3 cent apparent spread can disappear quickly. If fees and slippage cost 2 cents and one leg only fills halfway, the trade may no longer have the shape you intended.

The biggest mistake in polymarket kalshi arbitrage is assuming that similar market titles mean identical contracts. These pairs can look close but behave differently: That difference can turn a hedge into two unrelated bets.

Before pairing two markets, compare: For active traders, this is not a small legal detail. It is the core of the trade.

Start with the boring part: read the rules. On Kalshi, review the market rules, rules summary, outcome criteria, and verification source. On Polymarket, read the full resolution rules, including source, end date, and edge cases.

Do not rely only on the market title. If the title says "Will X happen?" but the rules say "according to Source Y by Time Z," the source and deadline are part of the trade.

Polymarket's documentation explains that displayed prices may reflect the midpoint of the bid/ask spread, while actual buying usually happens at the ask and selling at the bid. Kalshi's order book help page also shows bids and asks as resting orders at specific prices and quantities. For arbitrage math, midpoint prices are not enough.

Use this structure: If the remaining spread is tiny, execution quality matters more than the original signal.

A market can show an attractive price for only a few contracts. Example:

The first 15 or 20 contracts may look profitable. A larger order may not be.

For size, calculate the weighted average fill price. Do not multiply the best price by your full intended position unless the order book actually supports it.

Kalshi's fees page says fees can vary by market and refers traders to the current fee schedule. Polymarket's fees documentation says fees are determined per market at match time and differ by category.

That means there is no safe shortcut. Check the fee treatment for the exact market and venue before assuming the spread survives. Also include:

The smaller the spread, the more these details matter.

Cross venue arbitrage is rarely simultaneous for ordinary users. You may fill one leg, then watch the other venue move before the hedge is complete. This matters most when:

A trade that was positive at the start can become a directional position if only one side fills.

You find a politics market on Kalshi and a similar one on Polymarket. YES is cheap on one side and NO is cheap on the other. The spread looks attractive.

Then you read the rules.

One market resolves based on final certification. The other resolves based on a named media source before a specific date. If the source calls the result early, delays the call, or changes language, the two markets may not behave as true opposites.

That is not clean arbitrage.

A market shows 47 cents, but the best ask is 51 cents. Another venue shows the opposite side at 50 cents, but the available size is small.

The visible spread came from displayed or midpoint prices. The executable spread does not exist.

The first few contracts create a real spread, but the next level in the book removes it. This can still be useful for very small size, but it is not scalable.

Thin liquidity also increases failed-fill risk. If one side fills and the other side moves, you are left with exposure.

A 2 cent spread can look meaningful. After venue fees, spread paid to cross the book, and a small amount of slippage, it can become zero or negative. For small spreads, do the fee math before celebrating the signal.

A market may be visible but not tradable for your account, location, wallet setup, or market status. Prediction market regulation and platform availability can vary by jurisdiction and change over time. Check access before assuming a cross-venue route is available.

If any answer is unclear, the result belongs in the research pile, not the trade log.