Polymarket vs Kalshi: A Deep Dive into Liquidity Mechanics

We analyzed over 12 months of order book data (January 2025 – February 2026) to understand how liquidity differs across the two largest prediction market platforms — and what it means for traders and arbitrageurs.

Prediction markets have exploded into a $50B+ annual volume asset class. Polymarket and Kalshi now dominate ~97% of the market, but they operate on fundamentally different mechanics. One is crypto-native and peer-to-peer. The other is federally regulated with institutional market makers. Liquidity — not just headline volume or probability — determines real execution costs, slippage, and arbitrage viability.

At EventGraph, we aggregate and normalize raw order books, open interest, and depth from both platforms in real time. This unified dataset let us run the first apples-to-apples liquidity comparison across identical events — matched elections, sports, macro, and geopolitics contracts. Here are the key findings.

Methodology

Using our cross-venue ingestion architecture, we:

• Matched 1,200+ comparable markets across venues
• Measured bid-ask spreads, order book depth at 1%/5% price impact, simulated slippage for $1k / $10k / $50k orders
• Tracked volume distribution, open interest correlation, and cross-venue arbitrage windows
• Covered the full 2025 election cycle through early 2026 sports and macro volatility

All data was pulled live via EventGraph's ingestion pipeline — no manual scraping required.

Key Findings

1. Raw Volume & Market Share

Kalshi edged ahead in total notional volume for 2025 (~$25B vs Polymarket ~$23B) and maintained the lead into February 2026 (~$9.8B monthly vs Polymarket's $7B+). Sports drove ~80% of Kalshi's volume; politics and crypto drove Polymarket's peaks — including $478M single-day records.

2. Bid-Ask Spreads

Polymarket consistently delivered tighter spreads on high-interest markets. Top 100 political and crypto markets averaged 0.2–0.5¢ spreads. Kalshi's top markets were wider: 0.5–1¢ for political contracts, 1–2¢ for sports. In niche markets, both widened to 3–10¢, but Polymarket's global trader base closed gaps faster after news events.

3. Order Book Depth & Slippage

Polymarket excelled for institutional-sized trades in politics and crypto — $50k+ orders often moved price <0.8% in top markets. Kalshi offered more consistent depth up to $10k thanks to dedicated market makers and CFTC oversight. Larger orders saw 1–2% slippage more frequently outside sports.

Open interest stayed neck-and-neck (~$400M each at peak), but Polymarket concentrated liquidity in fewer, higher-stakes contracts.

4. Category Breakdown

• Politics & Elections: Polymarket advantage — tighter spreads, faster depth recovery after polls and breaking news.
• Sports: Kalshi's regulated order book and market makers delivered more reliable fills.
• Macro / Geopolitics: Cross-platform arbitrage windows appeared 2–5% of trading days when one venue lagged in depth.
• Niche Events: Both platforms thin. $1k trades could move prices 2–5%.

What This Means for Traders

Retail traders (<$5k): Polymarket often wins on lower effective cost — tighter spreads with no traditional fees beyond Polygon gas.

Institutions & funds: Kalshi's regulatory clarity and consistent market-maker depth reduce compliance risk. Polymarket offers deeper pockets on global events.

Arbitrageurs: Liquidity mismatches create genuine edges. We detected multi-percentage-point probability divergences with executable depth multiple times per week — but only if you monitor both order books simultaneously. Manual monitoring is impossible at scale.

In short: headline probabilities look similar, but real P&L is determined by liquidity mechanics. Ignoring depth and slippage is the fastest way to erode edge.

How EventGraph Helps

This entire analysis was only possible because of our unified platform. EventGraph solves the core problem every trader faces: fragmented data across incompatible venues.

• Cross-venue market aggregation — see the same event on Polymarket and Kalshi side-by-side
• Real-time liquidity and depth insights — spread alerts and slippage simulators
• Arbitrage detection — automated flags when spread + depth = profitable opportunity
• Market screener — filter by volume, liquidity score, or category

We operate the exact pipeline we used for this research: raw ingestion → normalization → gold-layer analytics. Available as a trader platform, data APIs, and an AI integration layer for LLMs and autonomous agents.

2026 Outlook

Liquidity across both platforms is improving rapidly as institutional capital flows in and regulation clarifies. Yet fragmentation persists. Prediction markets are becoming the "Bloomberg terminal" signal for elections, economics, and global events — but only if you can see the full picture.

EventGraph is building exactly that infrastructure layer.

All data derived from EventGraph's proprietary aggregation of public Polymarket and Kalshi order books. Past performance is not indicative of future results. Trade responsibly.