Polymarket vs Kalshi: Complete 2025 Comparison for Traders & Builders

Polymarket and Kalshi are the two dominant prediction market platforms, together processing over $28 billion in trading volume through 2025. But which platform is right for you? This comprehensive comparison covers fees, APIs, regulation, liquidity, and builder programs to help traders and developers choose the right platform.

Platform Architecture: Crypto vs Traditional Finance

The fundamental difference between these platforms lies in their architecture. Polymarket is built on blockchain technology with USDC on Polygon, while Kalshi operates as a traditional CFTC-regulated exchange using USD.

Fee Comparison: 120x Difference

The fee structures are dramatically different, making Polymarket significantly cheaper for high-volume traders:

Polymarket Fees

• International Platform: 0% trading fees (completely free)
• Polymarket US (launching): 0.01% flat fee (1 cent per $100 traded)
• Gas Fees: Covered by Polymarket's relayer for builder code transactions

Kalshi Fees

• Average Fee: ~1.2% per contract (varies by odds)
• Withdrawal: $2 ACH fee
• Comparison: 120x higher than Polymarket US's 0.01% fee

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API and Developer Experience

Both platforms offer robust APIs, but they cater to different developer audiences. Learn more in our Polymarket API guide.

Polymarket CLOB API

• Architecture: Hybrid off-chain order matching + on-chain settlement
• SDKs: py-clob-client (Python), @polymarket/clob-client (TypeScript)
• WebSocket: Real-time feeds via CLOB and RTDS endpoints
• Authentication: HMAC signatures with API keys
• Unauthenticated Access: Read-only operations available without API key
• Builder Integration: Builder codes for revenue sharing

Kalshi API

• Architecture: Traditional REST API with WebSocket support
• SDKs: kalshi-python (v2.1.4), Rust crate for async trading
• Authentication: API tokens expire every 30 minutes (requires re-login)
• Tiered Access: Different rate limits and capabilities by tier
• Demo Environment: Testing sandbox available

Trading Volume and Liquidity

Both platforms have seen explosive growth, with combined volume exceeding $28 billion through October 2025.

Polymarket Volume

• 2024 Total: ~$9 billion (up from $73M in 2023)
• Peak Month: $2.63 billion (November 2024)
• 2025 YTD: $7.5 billion+ (through August)
• Election Market: $3.3B on Trump vs Harris alone
• Peak Open Interest: $510M (November 2024)

Kalshi Volume

• 2024 Total: $1.97 billion (10x increase from 2023)
• Market Share: 62.2% of global prediction markets (up from 3.1%)
• Monthly Record: $4+ billion (October 2025)
• All-Time Volume: $16.2 billion cumulative
• Sports Markets: 70%+ of volume

Liquidity Providers

Kalshi has Susquehanna International Group as an official market maker since April 2024. Polymarket relies on decentralized liquidity providers and has seen $20M+ earned by LPs in 2024. For strategies, see our market making guide.

Market Coverage and Categories

Resolution Mechanisms

How markets resolve is critical for traders and arbitrage strategies. The platforms differ significantly:

Polymarket Resolution (UMA Oracle)

• System: UMA Optimistic Oracle with MOOV2 (whitelisted proposers)
• Process: Proposer submits → 2-hour challenge period → Auto-accepts if no dispute
• Dispute: UMA DVM with 48-hour tokenholder voting
• Philosophy: "Spirit of the market" over technical rules
• Success Rate: 98% settle without dispute

Kalshi Resolution (Centralized)

• System: Centralized editorial decisions
• Sources: White House, New York Times, official sources
• Process: Clear rules with named resolution sources
• Philosophy: Strict criteria, less interpretation
• Reliability: Generally more consistent

Regulatory Status

Polymarket Regulatory Journey

• 2022: $1.4M CFTC settlement, blocked US users
• 2024: FBI raided founder's home, DOJ investigation
• July 2025: DOJ and CFTC ended investigation
• September 2025: Purchased QCEX LLC for $112M (CFTC-licensed)
• November 2025: Granted DCM (Designated Contract Market) status
• Current: Operating regulated US exchange + international platform
• Advisor: Donald Trump Jr., J. Christopher Giancarlo (former CFTC Commissioner)

Kalshi Regulatory Status

• 2020: First CFTC-designated DCM for event contracts
• 2024: Won federal court battle for political contracts
• December 2025: CNN exclusive partnership ($11B valuation)
• Challenges: Fighting state-level restrictions (Connecticut, Nevada)
• Current: Federally regulated, institutional backing

For detailed regulatory analysis, see Is Polymarket Legal?.

Builder and Affiliate Programs

Polymarket has a robust Builders Program while Kalshi focuses on B2B partnerships.

Polymarket Builders Program

• Grants: $2.5M+ distributed, $100-$75,000 per project
• Revenue Model: Weekly USDC rewards based on volume
• Gas Subsidy: Polymarket covers all gas fees for builders
• Top Builder: Betmoar with $50M+ volume, 70% market share
• Current Volume: ~$20M weekly across 20+ builders
• Growth Potential: Only 2.5-3% of total volume (10x upside)

Kalshi Programs

• Referral: $10 flat bonus per qualified referral (100 trades in 30 days)
• Volume Incentive: Up to $0.005 per contract for high-volume traders
• Liquidity Program: $10-$1,000 daily rewards for market makers
• B2B Partnerships: Robinhood, Webull, PrizePicks integrations
• No Revenue Share: No percentage-based affiliate model

Cross-Platform Arbitrage Opportunities

Price discrepancies between Polymarket and Kalshi create arbitrage opportunities, but with significant caveats.

Arbitrage Tools

• EventArb: Free web calculator comparing Polymarket, Kalshi, Robinhood, PredictIt
• Polymarket Analytics: Unified view of cross-platform markets
• Custom Bots: Automated systems for capturing price differences

Example Arbitrage Setup

Bitcoin Reserve Market (hypothetical):

• Polymarket: 51% Yes
• Kalshi: 37% Yes (63% No)
• Combined: 51% + 63% = 114% (>100% = arbitrage opportunity)

Fee Impact on Arbitrage

A 3% gross arbitrage opportunity becomes:

• Polymarket International + Kalshi: 3% - 0% - 1.2% = 1.8% net
• Polymarket US + Kalshi: 3% - 0.01% - 1.2% = 1.79% net
• After resolution risk premium: Often not worth it

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Which Platform Should You Choose?

Choose Polymarket If:

• You want 0-0.01% trading fees (120x cheaper than Kalshi)
• You prefer no KYC and wallet-based access
• You're comfortable with crypto (USDC, MetaMask)
• You trade crypto, international politics, or culture markets
• You want to build tools with revenue sharing potential
• You value decentralization and blockchain transparency

Choose Kalshi If:

• You want CFTC regulatory protection
• You prefer USD and ACH/card funding
• You focus on US politics, economics, and sports
• You need clear, consistent resolution mechanisms
• You want institutional legitimacy (CNN partnership)
• You're building traditional fintech applications

Use Both Platforms If:

• You want to capture cross-platform arbitrage (with caution)
• You need comprehensive market coverage
• You're hedging between regulatory environments
• You're researching prediction market infrastructure

Future Outlook: 2025 and Beyond

Both platforms are positioned for massive growth as prediction markets enter the mainstream:

• Traditional Entrants: DraftKings, FanDuel, and Fanatics entering prediction markets
• Media Integration: Kalshi's CNN partnership bringing real-time odds to broadcasts
• Polymarket US: Re-entry with 0.01% fees could shift market dynamics
• Builder Ecosystem: Polymarket builders at 2.5% penetration vs Hyperliquid's 40%—10x growth potential
• Regulatory Clarity: Both platforms now CFTC-approved, reducing uncertainty