The 30-second answer
- Pick Polymarket for the widest market menu (politics, crypto, sports, culture), the deepest books on flagship events, and zero per-trade fees. Best for non-US traders or anyone willing to operate in USDC on Polygon.
- Pick Kalshi for US legal clarity (CFTC- regulated), USD settlement, and the tightest pricing on US macro events — Fed decisions, CPI, jobs, weather.
- Use both if you trade for a living — cross- venue arbitrage on shared events (rate decisions, elections) is a recurring edge.
What each platform actually is
Polymarket is a non-custodial prediction market on Polygon. You deposit USDC into your own wallet and trade binary YES/NO shares against an order book. Markets resolve through the UMA optimistic oracle. Polymarket is geo-blocked in the United States following a 2022 CFTC settlement.
Kalshi is a CFTC-regulated Designated Contract Market — a fully licensed US exchange for event contracts. You fund a brokerage-style account with USD via ACH and trade contracts that settle in cash. Kalshi is legal across all 50 US states and reports to the CFTC.
Both products are binary event contracts: every share you buy pays $0 or $1 depending on the outcome, and the live price is the market's implied probability between those two states.
Trading fees and costs
Polymarket charges no per-trade commission. Your costs are the bid/ask spread and Polygon gas on deposits, withdrawals, and trade settlement — generally a few cents per action. Liquidity providers earn the spread, not a fee rebate.
Kalshi charges a tiered taker fee scaled to the contract's expected profit — roughly 1–7% of (1 − price) × contracts for YES buys, with a cap per side. Makers (resting limit orders that get filled) usually pay no fee. The result: Kalshi is meaningfully more expensive on contracts trading near 50¢ and competitive — sometimes cheaper than the spread alone — on contracts trading at 5–10¢.
Withdrawals. Polymarket is bridge gas only. Kalshi is free for ACH and $25 for a wire.
Liquidity and book depth
Liquidity is event-specific, not platform-wide. The honest picture by category:
- Politics & elections. Polymarket wins by an order of magnitude on global elections; Kalshi is closer on US-only races and has exclusive US-listed contracts on congressional control.
- US macro (Fed, CPI, jobs). Kalshi has designated market makers paid to quote tight, so spreads routinely sit at 1–2¢ even days before resolution.
- Crypto, sports, culture. Polymarket only — Kalshi has limited listings here.
- Weather. Kalshi only.
- Long-tail markets. Both thin out below $100K notional. Trade small or use limit orders.
For Polymarket liquidity in real time, the whale leaderboard shows which markets the top 50 wallets are buying — a clean proxy for where the deep money sits.
Supported market types
| Dimension | Polymarket | Kalshi |
|---|---|---|
| Settlement currency | USDC (stablecoin) | USD (bank/ACH) |
| Trading fees | 0% — spread only | Tiered 1–7% of expected profit, capped |
| Withdrawal cost | Polygon gas (~$0.01–$0.10) | Free ACH; $25 wire |
| Order types | Limit, market, GTC | Limit, market, GTC, fill-or-kill |
| Resolution oracle | UMA optimistic oracle | Internal review (CFTC-regulated) |
| Regulation | Geo-blocked in US (CFTC settlement) | CFTC-regulated DCM, US-legal |
| Top monthly volume | Politics, crypto, sports, culture | Fed, CPI, weather, elections |
| Account opening | Crypto wallet (Polygon) | US SSN + bank account |
| Best for | Global traders, broad market menu | US traders, macro/economic events |
Access, custody & regulation
Polymarket is non-custodial — your USDC sits in a wallet you control. The flip side is that the platform is geo-blocked for US users; circumventing the block violates the TOS and is a CFTC issue, not just a product one. You bring your own self-custody discipline.
Kalshi is custodial and regulated — your USD sits in a segregated customer account at a US bank, and trades clear through a CFTC-supervised exchange. You give up self-custody and pay for the regulatory wrapper with fees, but you get FDIC pass-through on cash balances and clear legal standing.
Simulated trading. FundMyOpinion sidesteps both questions — you trade a virtual account against live Polymarket prices, no wallet or US bank required. It's the fastest way to test a strategy on real prices without committing capital to either venue.
How to choose
- If you live in the US and want to trade with real money: Kalshi. It's the only one you can legally use directly.
- If you trade global events (non-US elections, crypto, sports, culture): Polymarket — Kalshi's catalog is too narrow.
- If you trade US macro (Fed, CPI, jobs, weather): Kalshi. Tighter spreads, real designated market makers.
- If you're not sure yet: practice on FundMyOpinion's simulator against live Polymarket data, then graduate to whichever real venue fits your jurisdiction and event mix.
Whichever venue you trade, the rules of survival don't change. Read the strategy guide for sizing, drawdown management, and finding edge in binary outcomes.