Combined monthly volume at Kalshi, Polymarket and Polymarket US fell 14.5% to $45.33 billion in August, the first decline since August 2025. The reading ended a year-long run of monthly growth after summer activity accelerated around the World Cup.
The figure tracks taker notional volume in U.S. dollars across the three venues, according to The Block Data's dashboard methodology. The August pullback was uneven, with Kalshi posting a substantially smaller decline than Polymarket and Polymarket US combined.
Data Snapshot
| Metric | Current | Previous | Change | Period | As of | Source |
|---|---|---|---|---|---|---|
| Combined monthly volume at Kalshi, Polymarket and Polymarket US | $45.33 billion | — | fell 14.5% | August 2026 | September 2, 2026 | The Block |
| Kalshi volume | $37.17 billion | $40.1 billion | down 7.3% | August 2026 vs. July 2026 | September 2, 2026 | The Block |
| Polymarket and Polymarket US combined volume | $8.16 billion | $12.89 billion | down 36.7% | August 2026 vs. July 2026 | September 2, 2026 | The Block |
| Combined prediction-market volume | $25.66 billion | — | — | May 2026 | September 2, 2026 | The Block |
Kalshi accounted for most August volume
Kalshi recorded $37.17 billion in August volume, down 7.3% from $40.1 billion in July, according to The Block. It was the largest contributor to the $45.33 billion combined total.
Polymarket and Polymarket US combined for $8.16 billion, down from $12.89 billion in July and representing a 36.7% decline. That contraction was substantially steeper than Kalshi's, concentrating more of the combined measure's August decrease in the two Polymarket venues.
The figures use the same measure—taker notional volume in U.S. dollars across the three venues—according to The Block Data's dashboard methodology, and are components of one combined monthly total rather than separate estimates based on different volume definitions.
Kalshi and Polymarket's combined volume falls 15% in August, first monthly decline in a year — Source: The Block
World Cup activity preceded the pullback
The World Cup ran from June 11 to July 19 and helped drive a summer spike in prediction-market activity.
When the tournament concluded, combined monthly volume at Kalshi, Polymarket and Polymarket US fell 14.5% in August to $45.33 billion. It was the first monthly decline since August 2025.
August nevertheless remained above May's $25.66 billion, leaving activity higher than it was earlier in the year.
State scrutiny of sports-related contracts
State regulators in the U.S. are intensifying scrutiny of Kalshi and Polymarket, especially over sports-related contracts. The Block reports that more than a dozen states have taken enforcement action or filed lawsuits against the companies.
The available volume data do not show that those actions caused August’s decline, which followed a World Cup-driven summer spike in prediction-market activity.
