Predictions.io Launches to Aggregate Data Amid Discrepancies in Prediction Markets

A new data aggregation platform, Predictions.io, has launched to provide traders with cross-venue comparison tools for the rapidly growing prediction markets. The service aims to highlight significant price discrepancies for identically worded contracts on major platforms like Kalshi and Polymarket, offering new insights as the industry experiences record trading volume and heightened regulatory attention.

Significant Price Gaps Revealed

The platform's analysis reveals that contracts on major political and economic events can trade at substantially different prices depending on the venue. According to data released by Predictions.io, two identically worded U.S. midterm election markets showed a price difference of 8.5 percentage points between Polymarket and Kalshi as of August 28.

This is not an isolated incident. The company reported that across a sample of directly comparable binary markets, the median price gap was more than four percentage points, with nearly half of the pairs differing by five points or more. Such discrepancies challenge the idea of a single "market-implied probability" for an event and may present arbitrage opportunities for sophisticated traders.

New Tools for Market Participants

Predictions.io is now tracking over 9,700 markets across Kalshi, Polymarket, and Manifold, covering categories from U.S. politics and economics to cryptocurrency and geopolitics. The platform has also released free tools to help users navigate the different fee and pricing structures of each venue.

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• Fee Calculator: This tool calculates the effective all-in price of a trade on each platform, accounting for complex fee formulas like Kalshi’s and comparing them to Polymarket’s structure.
• Odds Converter: A utility to convert between American, decimal, and fractional odds and their implied probabilities.

"A single venue’s price is a data point. The spread between venues is the information," a spokesperson for Predictions.io said in a statement. The company stressed it operates as a neutral data service and is not an exchange, broker, or investment adviser.

Context: Record Volume and Regulatory Headwinds

The launch comes at a pivotal time for the prediction market industry. Combined trading volume for Kalshi and Polymarket reached a record $50.59 billion in July, according to the press release, with Kalshi representing approximately 74.5% of that total. This growth has attracted increased scrutiny from regulators, including a probe in New York City and a review by the Commodity Futures Trading Commission (CFTC).