If you're new to prediction markets, the two names that come up most often are Polymarket and Kalshi. They're both legitimate venues with real liquidity and real users, but they're built on very different foundations and they serve different audiences. This is a short, neutral side-by-side to help you figure out which one fits what you're trying to do.
The short version
Polymarket is an on-chain prediction market built on the Polygon sidechain. You deposit USDC into a self-custodied wallet and trade binary outcome tokens on a central limit order book. It's not available to users in the United States.
Kalshi is a CFTC-regulated event contract exchange based in the United States. You open an account the way you'd open a brokerage account, fund it with USD through a bank or card, and trade regulated event contracts. It's primarily for US users.
If you can use either, the question is less about which is "better" and more about what you care about: custody model, market breadth, regulatory comfort, and whether you plan to automate.
Markets and liquidity
Both venues cover a lot of the same ground — elections, sports, macro events, occasional pop-culture questions — but their depth varies by topic. Kalshi tends to have strong liquidity in US-centric questions (domestic politics, Fed decisions, US sports) because that's where its user base concentrates. Polymarket's user base is global, so its liquidity skews toward questions with international resonance: world politics, crypto, geopolitics, major sports tournaments with worldwide audiences.
If you're looking at an obscure long-tail market, check both and see which one has tighter spreads before committing capital. Neither is uniformly better.
Fees
Fee structures change often enough that it's worth reading each platform's current fee page rather than quoting numbers that could be stale. In broad strokes: Polymarket's fees are on the taker side and relatively small, and makers often pay nothing. Kalshi's fees vary by contract and are embedded in the trade. Factor in whatever funding costs you incur getting money in and out — for Kalshi that's bank-side; for Polymarket it's the gas and bridging cost of getting USDC onto Polygon.
Custody and keys
This is the biggest philosophical split.
On Polymarket your positions live on Polygon. If you use the Magic.link login, your wallet is generated for you, but you can export the private key and move your funds. This is self-custody with training wheels, and it means the platform can't freeze your balance or close your account and keep your money. It also means if you lose your key you lose your funds — the usual crypto trade-off.
On Kalshi your positions live in a brokerage account. The exchange is the custodian. If you forget your password you can reset it, and if the exchange is compelled by a regulator to act on your account, it can. For some users that regulatory backstop is a feature; for others it's a bug.
Regulation
Kalshi is regulated by the CFTC as a Designated Contract Market. That puts it in the same category as commodities and futures exchanges. It's the most formally sanctioned prediction market in the US.
Polymarket is not a US-regulated entity and is not available to US users. It operates as a decentralized platform on Polygon. Regulators in other jurisdictions take different views, so if you're outside the US, check your local rules.
API and automation
Both platforms have APIs. Polymarket's CLOB API is well-documented and widely used by third-party tools — bots, dashboards, copy traders. Because the order book is on-chain and there's a public mempool on Polygon, you can also watch for pending orders in a way that isn't possible on a traditional centralized exchange.
Kalshi has a REST and WebSocket API, but automated trading on it is scoped to what their terms allow. Read the developer agreement before you build anything production.
Which fits you
- You're in the US and want event exposure inside a regulated account. Kalshi.
- You're outside the US and want broader market coverage, especially in crypto and global politics. Polymarket.
- You want to self-custody and build automation on top. Polymarket, because of the on-chain structure and mempool visibility.
- You don't want to touch crypto or manage keys. Kalshi.
Where PolyZig fits
PolyZig is a copy-trading layer on top of Polymarket. We chose Polymarket specifically because of the on-chain order book and the public mempool — those are the properties that make sub-second copy execution realistic. None of this would translate cleanly to a closed venue. That's not a knock on Kalshi; it just means they're tools for different jobs.
If you're deciding where to start, our honest advice is: pick the one that matches your jurisdiction and risk tolerance, size small for the first few weeks, and don't confuse "this platform is regulated" or "this platform is decentralized" with "this platform will make me money." Both are venues. The edge, if there is one, comes from what you do inside them.