Polymarket traded $4.5B in the last 30 days, down 8%, for just 5% share as Kalshi holds 76%

Polymarket’s rolling volume declines

Polymarket recorded $4.5B in contract trading over Sep 15-Oct 14, 2026, according to defirate.com. That was down 8% from the preceding 30-day period.

The platform represented 5% of prediction-market volume in the snapshot. Kalshi held 76%, leaving a substantial gap between the two platforms’ shares of reported activity.

Two measures of trading activity

Defirate.com also reported $2.3B in dollars paid for Polymarket over the same period. That figure is distinct from the $4.5B contract-volume measure; the two should not be treated as interchangeable.

The figures describe a rolling 30-day window, rather than a single day’s activity. They establish a decline in Polymarket’s reported volume, but the supplied data do not explain what drove it or show how its market share changed from the previous period.

What it means for prediction markets

• Platform activity is unevenly distributed: Polymarket’s 5% share contrasts with Kalshi’s 76%, making the venue important context when assessing overall market activity.
• Metric definitions matter: The $4.5B in contracts and $2.3B in dollars paid describe different measures, so comparisons require a consistent basis.
• The decline has limits as a signal: The 8% drop measures Polymarket’s volume change, not a shift in event probabilities or evidence of weaker liquidity in any particular contract.