Prediction Market Arbitrage Is Real and Here Is How to Find It
Arbitrage is one of those finance words that gets thrown around loosely but has a precise meaning; it is a trade where you lock in a guaranteed profit with no risk, by exploiting a price discrepancy across two markets. Pure arbitrage is rare and usually disappears fast. But in prediction markets, where the same event is priced simultaneously on multiple platforms with different liquidity and different participant bases, discrepancies appear more often than you would expect.
When Polymarket prices an event at 55% and Kalshi prices the same event at 48%, someone who buys Yes on Kalshi and No on Polymarket (or vice versa) is hedging across both markets. If the two prices together allow all outcomes to pay out profitably, that is an arbitrage. You win regardless of what actually happens.
The FatNarwhal Arbitrage Finder takes prices from two or more markets on the same event and tells you whether an arbitrage exists, how much you need to bet on each side, and what your guaranteed profit looks like after all positions are settled.
How to Use It
Go to fatnarwhal.com/arbitrage and enter the prices for both sides of an event across two markets.
Let's use a clean example. Say a market on who wins a specific Senate seat is priced at 60 Yes / 41 No on Polymarket (prices do not have to sum to 100 exactly, there is a spread), and the same event on Kalshi shows 57 Yes / 45 No.
Enter those four numbers into the tool. It calculates whether there is a combination of bets across both platforms that pays out more than you put in regardless of the outcome. It tells you the exact bet sizes to place on each side, the total amount you need to stake, and the guaranteed return if an arb exists.
If there is no arb, the tool shows you how close you are to one; sometimes the gap is small enough that one platform shifting a point or two would open it up, which tells you when to check back.
The Math Behind It
An arbitrage exists when the combined cost of covering every outcome comes to less than the guaranteed payout. Working in implied-probability terms — if you can buy Yes at implied probability on one platform and buy No at implied probability on another, an arbitrage exists when:
Because you would be paying less than a dollar total for a position that pays out a dollar regardless of which side wins. Your profit is per dollar of exposure.
The tool calculates the optimal stake on each side to equalize the payouts regardless of outcome, and computes the net return.
When to Use It and When Not To
Use it any time the same binary event is live on multiple platforms simultaneously. The best opportunities tend to appear right after breaking news, when different markets update at different speeds. Check the tool when a market moves sharply on one platform and you suspect the other has not caught up yet.
A few practical realities to keep in mind. Prediction market arbs are often smaller than they appear once you account for fees, withdrawal delays, and the fact that you need capital sitting idle on multiple platforms simultaneously. The opportunity can close before you execute both legs, since markets move and the arb disappears the moment other traders notice it too. Some platforms also have position limits or resolution rules that differ subtly enough to make what looks like the same event actually a different bet.
True arbitrage also requires both legs to be executed; if you get filled on one side but the other side moves away from you before you can complete it, you are no longer hedged. That is called execution risk and it is real.
Try It
Next time you are watching a major event unfold in real time across multiple prediction markets, pull up fatnarwhal.com/arbitrage and enter the live prices. Arbs close fast; the tool tells you instantly whether one exists and exactly how to execute it.
Risk-free profit sounds too good to be true. Occasionally it is not.