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Markets4 min read

Prediction market data: where to get it and how to use it

Where to get prediction market data from Kalshi and Polymarket, free APIs and paid feeds, how to read prices as probabilities, and pitfalls to avoid.

By Kristian FagerlieFounder & CEO, Sikt Intelligence

Prediction market data is the price history of bets on real-world events, and each price is a probability. A contract trading at 64¢ says the market sees a 64% chance. That makes the data unusually useful: live, tradable probabilities on elections, Fed decisions, recessions and geopolitics, updated by the minute. Here is where to get it, how to use it, and the mistakes that ruin most analyses.

What the data contains

  • Prices: the last trade, the best bid and ask, or the midpoint between them. Each can be read as a probability.
  • Price history: how the probability moved over time, often in daily or hourly steps.
  • Volume and open interest: how much money is behind a price. A thin market's price is a much weaker signal.
  • Order books: what traders are willing to pay at each price, which shows how far the price would move on a large trade.
  • Rules: exactly how the market resolves. Two markets with similar titles can ask different questions.

Where to get it

Kalshi

Kalshi, a US exchange regulated by the CFTC, offers a public REST API (Kalshi docs). Market data, including events, markets, prices and daily price history ("candlesticks"), can be read without an account or API key; trading requires one.

Polymarket

Polymarket offers two public APIs (Polymarket docs): one for events and markets, including titles, outcomes and rules, and one for order books, prices and price history. Because Polymarket settles on the Polygon blockchain, every trade is also public on-chain, which analysts use for questions such as who trades and how much.

Institutional feeds

For professionals, the data is now packaged like any other market data. In February 2026, Intercontinental Exchange (ICE), the owner of the New York Stock Exchange, launched Polymarket Signals and Sentiment: normalized prediction market feeds, including historical data for backtesting (Markets Media). We cover how funds use it in how hedge funds and quant firms use prediction markets.

Ready-made views

If you just want to see the numbers, our odds pages put Kalshi and Polymarket side by side on the biggest events, from Fed rate odds and recession odds to the 2026 midterms, with 90 days of price history, refreshed every 6 hours.

How to use it

  1. As probabilities. Read the price as the market's chance, after allowing for the spread and fees. We explain the math in prediction market odds, explained.
  2. As a risk input. A live probability on a Fed decision or a recession is something most other assets do not price directly. See will the Fed raise rates in October? and recession odds for 2026 and 2027.
  3. To measure news. Look at how the probability moved around an announcement. A jump from 30% to 70% after a jobs report tells you how much the market thought that report mattered.
  4. To compare venues. When Kalshi and Polymarket price the same event differently, the gap usually comes from different rules or a thin market, and occasionally from real disagreement.
  5. As a benchmark. Score any forecaster, human or AI, against the market's prices on the same questions. Our free Brier score calculator takes a third column for the market's probability and shows your skill against it.

Pitfalls that ruin most analyses

  • Long shots are overpriced. Contracts under 10¢ win less often than their price suggests: on Kalshi, buyers of such contracts lost more than 60% of their money on average (Bürgi, Deng and Whelan). Do not read a 5¢ price as a 5% chance without thinking. See the favorite-longshot bias.
  • Thin markets. A price set by a handful of small trades can be stale or easy to move.
  • Which price? Last trade, midpoint and best ask can differ by several points on a quiet market. Be consistent.
  • Rules, not titles. Check the resolution source and deadline before comparing markets; see event contracts, explained.
  • Survivorship. Markets that were created, delisted or merged can disappear from simple queries, which biases studies of accuracy.
  • Time zones and timestamps. Align prices to the moment news broke, in the same time zone, or event studies go wrong.

Where Sikt Intelligence fits

Market data tells you what traders think. Sikt Intelligence is building the second number: an AI superforecaster that reads the news and data that exist today, checks every source, and puts an honest probability next to the market's price, so the gap between the evidence and the traders is visible at a glance. Its first public test is the Sikt Midterm Bench, next to Kalshi and Polymarket. If you work in research, risk or trading, leave your email below for early access. Nothing here is financial or investment advice.

Key takeaways

  • Prediction market prices are probabilities, with history, volume and order books behind them.
  • Kalshi and Polymarket both offer public APIs for market data; ICE packages Polymarket data for institutions.
  • Use the data as probabilities, risk inputs, news measures, venue comparisons and forecasting benchmarks.
  • Watch for long-shot bias, thin markets, inconsistent prices, rule differences, survivorship and timestamps.

FAQ

Where can I get prediction market data?

From the venues' own APIs: Kalshi's public REST API and Polymarket's public market and price APIs. Institutions can buy normalized Polymarket feeds from ICE. For a quick view, our odds pages show Kalshi and Polymarket side by side with 90 days of history.

Is prediction market data free?

Market data from the Kalshi and Polymarket APIs can be read for free; trading requires an account. Institutional feeds with normalized and historical data are paid products.

How do I turn a prediction market price into a probability?

Divide the price by the payout: a contract that pays $1 and trades at 64¢ implies about a 64% chance. Adjust for the spread, fees and the long-shot bias before relying on it.

Does Kalshi have an API?

Yes. Kalshi offers a public REST API; market data such as events, prices and daily price history can be read without an API key, while trading requires an account.

Sources

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