Picking a prediction market platform is not just about which one lists the contract you want. The platform itself shapes how you trade, and that quietly bleeds into your returns, the strategies you can run, and even which questions are legal to bet on in the first place.
Regulation, and what it costs you
Kalshi runs as a CFTC-regulated designated contract market in the US, so it sits under the same framework as futures exchanges. You get legitimacy and legal clarity. The tradeoff is that the CFTC has historically blocked whole categories of contracts, especially around elections and specific political events, though that has been loosening.
Polymarket is offshore and mostly unregulated, which buys it a lot of freedom in what it can list. Political markets, crypto events, niche cultural questions, almost anything can become a market. US residents are technically restricted, though enforcement has been spotty. Settlement happens on-chain via Polygon, which adds transparency but also gas costs and the usual wallet-management overhead.
Manifold goes a completely different direction. It runs on play money by default, which sidesteps regulation entirely. Anyone can spin up a market on anything. Quality is all over the map, but the sheer number of unique questions is unmatched. Manifold has added real-money markets selectively, but play money is still the core of it.
Fees and where they eat your edge
Kalshi charges no trading fees on most contracts and instead builds its margin into the spread. What you actually pay depends on liquidity, but for popular markets it usually runs 1 to 3 percent round trip. ACH withdrawals are free.
Polymarket has no explicit trading fees either, but there's a spread baked into the AMM pricing, plus Polygon gas on every transaction. On small trades the gas is fractions of a cent. If you're doing hundreds of trades it adds up, but it stays well under what a centralized platform would charge.
Manifold's play-money markets use a loan system that pays your stake back over time from resolved bets, which creates a genuinely different incentive structure. The fee setup on its real-money markets is still a moving target.
The practical version of all this: if your edge on a trade is under 3 percent, fees will eat most of it no matter where you trade. That's why serious traders drift toward higher-conviction positions instead of grinding out high-frequency ones.
Liquidity and market coverage
Polymarket wins on raw volume, regularly clearing billions a month across its busiest contracts. Its deepest books, usually US politics and big crypto events, can swallow six-figure orders with barely any slippage.
Kalshi's books are thinner on most contracts, but it lists markets that don't exist anywhere else, particularly around economic data releases, weather, and regulatory outcomes. Its liquidity is climbing but still sits an order of magnitude below Polymarket's top markets.
Manifold is thin almost everywhere because it's fragmented across thousands of user-created questions. That fragmentation is also the point. If you have a view on some obscure topic, odds are someone on Manifold already made a market for it.
How the contracts themselves are built
Kalshi uses standardized event contracts with fixed expirations and clear resolution sources, and each one goes through compliance review before it lists. Fewer markets, but the resolution criteria are tight.
Polymarket is more mixed. Some markets are specified cleanly with clear sources. Others have fuzzy criteria that have triggered resolution disputes. The specification process has gotten better over time, but reading the resolution rules carefully before you put money down is still on you.
Manifold lets anyone create and resolve markets, so resolution quality comes down entirely to the creator. There's a reputation system to flag the unreliable ones, but disputes are more common here than on either of the others.
Which one fits how you trade
For putting serious capital on high-profile events, Polymarket's liquidity is hard to beat. For regulated exposure with clean tax reporting, Kalshi is the easy call. For poking at niche questions, testing your calibration, or trading topics no regulated venue would ever touch, Manifold covers the gap.
Plenty of active traders just run all three, treating each platform's unique coverage as more surface area to find edge. It also means that when the same question is priced differently across venues, there's an arbitrage sitting there. If you're going to bet across all three, the one habit worth building is checking the resolution criteria on every contract before you size in, because that's where the surprises usually hide.