The short answer
Use Kalshi if you're in the US and want a regulated, dollar-denominated exchange with clean tax paperwork and deep markets in economics, weather, politics and sports. Use Polymarket if you want the widest market selection, crypto rails, and the biggest pools of liquidity on major global events. Serious traders keep accounts on both and route each trade to whichever venue prices it worse.
Side-by-side
Regulation and status
- Kalshi is a CFTC-regulated designated contract market — a licensed US derivatives exchange. Contracts are legal financial instruments, not bets.
- Polymarket is a crypto-native prediction market that settles on-chain. Its availability and features differ by jurisdiction, and access rules have changed repeatedly.
- If regulatory certainty matters to you — because you're trading size, or you need documentation — Kalshi is the conservative choice.
Money in and money out
- Kalshi: US dollars, via bank transfer, debit card or wire. Balances are in USD; no crypto knowledge needed.
- Polymarket: USDC on a low-fee chain. You need a wallet, and you pay network fees to move funds — trivial in dollars, but a real friction if you've never used crypto.
- Withdrawal speed usually favours Polymarket (minutes), while Kalshi runs on banking hours.
Fees — the part that decides your edge
Kalshi charges a per-trade fee that scales with contract price, peaking near 50¢ where uncertainty is highest. Polymarket has historically charged no maker/taker fee on most markets, taking its cost out of the spread instead. That has a concrete consequence: on near-coinflip markets, Kalshi's explicit fee can be the largest single drag on your returns, while on thin Polymarket markets the invisible cost is the spread you cross.
Always price the round trip before you enter. A 2¢ spread plus a 1¢ fee means a contract at 50¢ needs your true estimate to be above roughly 53¢ to be worth taking.
Liquidity and market selection
- Polymarket generally wins on headline global events — elections, geopolitics, crypto prices, culture — where order books get very deep.
- Kalshi wins on US economic data (CPI, Fed decisions, jobs numbers), weather, and an expanding sports slate, where it is often the only regulated venue.
- Both have long tails of thin markets. Depth, not the venue's name, is what determines whether you can actually get filled at your price.
When each venue is better
- Trading US macro releases: Kalshi, almost always — the markets are purpose-built and settlement is unambiguous.
- Trading a big global news event with size: Polymarket, for depth.
- Arbitraging the two against each other: keep balances on both. The same event is frequently priced 2–5¢ apart, and that gap is one of the most reliable edges available to a retail trader.
- You want zero crypto exposure: Kalshi.
The cross-venue arbitrage, concretely
Suppose an event trades at 61¢ YES on Polymarket and 56¢ YES on Kalshi. Buying YES on Kalshi and NO on Polymarket at 39¢ costs 95¢ for a position that pays exactly $1 at resolution — about 5¢ of gross edge, minus fees and the capital you tie up until the market settles. It sounds free, and mostly it is, but three things eat it: the Kalshi fee, the spread you cross on both legs, and the risk that the two venues word their resolution criteria differently. Read both rulebooks before you assume the legs cancel.
Resolution risk is the risk everyone forgets
The single most common way traders lose money on a "correct" prediction is a resolution clause they never read: which source counts, what happens on a tie, how a cancelled event settles. On regulated venues the rules are published and enforced; on any venue, the rule text — not your intuition about the event — is what pays you.
Next steps
If you're new to either platform, start with how Polymarket works and how Kalshi works, then look at Bitcoin prediction markets for a concrete pricing example.