Kalshi vs Polymarket: Which Prediction Market Is Better for Traders?

What each platform is

Kalshi

Kalshi is a federally regulated event contracts exchange, registered with the Commodity Futures Trading Commission (CFTC) as a Designated Contract Market. It launched in 2021 and was the first US-regulated prediction market to receive CFTC approval for event contracts across categories including economic data, politics, and weather.

Because Kalshi is CFTC-regulated, it operates like a financial exchange. Contracts are denominated in dollars, settle between $0 and $1, and are traded on a central limit order book with a market maker. US residents can participate fully, and Kalshi is accessible under standard financial account rules.

Polymarket

Polymarket is a blockchain-based prediction market built on the Polygon (MATIC) network. It launched in 2020 and is not registered with US financial regulators; in fact, US residents are officially excluded from the platform under its terms of service, though enforcement is limited. Polymarket uses USDC (a USD-pegged stablecoin) for all transactions, and contracts are settled by a decentralized oracle network (UMA Protocol).

Polymarket has no central order book in the traditional sense. It uses automated market makers (AMMs) for liquidity, supplemented by a limit order book for larger trades. It's global by default, with no geographic restrictions for non-US users.

Regulation and US access

For US-based traders, Kalshi is the clearly compliant option. Polymarket's data is freely accessible via its public API regardless of where you are, which means you can use Polymarket prices as an information source without participating directly: the prices are public, CORS-open, and queryable from any HTTP client.

Liquidity and volume

Polymarket has historically had higher total volume than Kalshi on high-profile political and macro events. The 2024 US presidential election drove record volumes on Polymarket (hundreds of millions of dollars in trading) because its global, permissionless nature attracted international participants. During major political events, Polymarket is often the deeper and more efficient market.

Kalshi's liquidity advantages appear in regulated categories where Polymarket can't legally operate within the US. For strictly financial event contracts (CPI, GDP, FOMC rate decisions), Kalshi tends to have better market depth from US institutional participants who can't use Polymarket.

Both markets suffer from liquidity gaps on niche or recently-created contracts. A market with less than $500K in total volume is likely too shallow for meaningful price discovery; spreads will be wide and prices more susceptible to manipulation. Focus on markets with $1M+ in volume for reliable signals.

Available markets

The market coverage is different in important ways:

For macro traders

Kalshi is typically better for US economic data events (CPI, FOMC, NFP). Their CPI market in particular is often the most liquid prediction market for that event, with $1–5M in volume per release and market maker participation from informed traders.

For political event traders

Polymarket tends to have more volume and international diversity on major political events, particularly non-US elections and geopolitical developments. The Trump vs Harris 2024 market on Polymarket was the largest prediction market in history, and the prices were widely cited as more accurate than polling averages.

For options flow cross-reference

Both platforms offer useful signals. Polymarket's free API makes it easier to automate monitoring. Kalshi's API requires authentication but covers more regulatory-compliant categories for US-based monitoring systems.

Fees and costs

Kalshi fees

Kalshi charges a trading fee on each transaction, calculated as a percentage of the contract value. As of 2026, Kalshi's standard fee is approximately 7% of the winning side's payout, paid on resolution. This is deducted from winnings; you don't pay if you lose. For a $100 contract that wins, you'd pay approximately $7 in fees and receive $93 in profit.

Kalshi periodically adjusts fees and offers rebates to liquidity providers who post limit orders that improve the book. Active traders who provide liquidity pay materially lower effective fees.

Polymarket fees

Polymarket charges approximately 2% of winnings on market resolution, paid to Polymarket and liquidity providers. The lower fee structure is one reason Polymarket attracts higher volume on competitive markets: the economics are better for frequent traders.

Polymarket also has implicit costs from the AMM structure: slippage on large trades moves the price against you. On deep markets (top-volume events), slippage is negligible; on shallow markets, a $10K trade can move prices materially.

API and data access

Polymarket API

Polymarket's API is completely open and requires no authentication for read access:

# Fetch active markets by volume (no API key needed)
curl "https://gamma-api.polymarket.com/markets?active=true&closed=false&limit=50&order=volumeNum&ascending=false"

Fields returned include current prices (implied probabilities), volume, liquidity, resolution date, and the question text. This makes Polymarket extremely easy to integrate into automated monitoring systems: no API keys, no rate limits for reasonable polling frequencies.

Kalshi API

Kalshi provides a REST API that requires authentication (API key). It's more structured than Polymarket's API, returning standardized financial data formats consistent with its regulated exchange status. Kalshi's API is better suited for order execution (placing trades) while Polymarket's is better for data extraction (reading prices as a signal).

# Kalshi API requires authentication
curl -H "Authorization: Token YOUR_API_KEY" \
  "https://trading-api.kalshi.com/trade-api/v2/events?limit=100&status=open"

For information arbitrage use cases

Polymarket's no-auth API is the better choice for traders who want to monitor prediction market prices as a background signal alongside options flow. Kalshi's API is better when you need CFTC-regulated economic data market prices specifically.

Accuracy and calibration

Both Polymarket and Kalshi have been studied for predictive accuracy. Research comparing both to polls, expert forecasts, and news consensus on major events (elections, central bank decisions, geopolitical outcomes) consistently finds that prediction market prices outperform alternative forecasting methods when markets are sufficiently liquid.

Important calibration nuances:

• Both platforms suffer from "longshot bias": low-probability events are slightly over-priced relative to their actual frequency. A 5% market rarely resolves at exactly 5%.
• Kalshi tends to be better-calibrated on economic data (CPI, FOMC) because it attracts more US institutional participants with macro models.
• Polymarket tends to be better-calibrated on political events (elections, geopolitics) because its global participant base includes more regional expertise on non-US events.
• Both improve with volume: a market with $5M in volume is far more accurate than one with $50K.

Which to use for different purposes

For US traders who want to participate directly

Use Kalshi. It's fully compliant, USD-denominated, and regulated. If you want to bet on CPI outcomes or Federal Reserve decisions with real capital, Kalshi is the clean option. The higher fees are the tradeoff.

For traders who want prediction market data as a signal (not to trade directly)

Start with Polymarket. The free, no-auth API makes it the easiest to integrate into a monitoring system. The signal quality on political and macro events is excellent. US-based traders can read Polymarket data freely, just not participate directly.

For monitoring Federal Reserve and economic data specifically

Use Kalshi. Their Fed Funds rate and CPI markets are typically deeper and more precisely structured than Polymarket's equivalents.

For maximum cross-domain flow signal quality

Monitor both. Polymarket for broad political/macro coverage, Kalshi for US economic data categories. When both platforms agree on a probability shift, the signal is more reliable than either alone. Cross-reference with unusual options flow in the affected equity sector for three-signal confluence.

Key takeaways

• Kalshi is CFTC-regulated and fully accessible to US residents; Polymarket is blockchain-based, global, and officially excludes US users (though data is freely accessible).
• Polymarket has higher total volume on political events; Kalshi has better liquidity on US economic data (CPI, FOMC).
• Polymarket fees (~2% of winnings) are lower than Kalshi's (~7%); Polymarket's API requires no authentication; Kalshi's API requires an API key.
• For signal-only use (monitoring prices without participating), Polymarket's free API is the easier integration; for US traders wanting to participate compliantly, Kalshi is the only legal option.
• Both platforms outperform polls and expert forecasts on well-liquid markets; calibration quality correlates strongly with trading volume.
• For cross-domain trading, combine prediction market signals from both platforms with unusual options flow for three-signal convergence setups.