The Volume Numbers Coming Out of Prediction Markets Are Not Comparable, and That Is a Problem

Prediction markets went from roughly $9 billion in combined global trading volume in 2024 to more than $40 billion across Kalshi and Polymarket in 2025. That figure gets quoted constantly. It is also assembled from numbers the two platforms do not define the same way.

Anyone trying to size this sector, compare venues or model where liquidity is actually sitting runs into the same wall that DeFi analytics hit five years ago. The headline metric is easy to publish and hard to trust.

Three Ways Volume Gets Counted

Start with what a platform means when it says volume.

Notional volume counts the full face value of every contract traded. A contract that settles at $1 and trades at 30 cents can be counted at $1 of notional or 30 cents of cash traded, and those produce very different totals for identical activity.

Matched volume counts only trades that actually cleared against a counterparty. Some venues report order flow that includes activity never matched, which inflates the figure without inflating the market.

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