Kalshi and Polymarket Open Interest Drops 20% After World Cup Frenzy
Open interest on prediction market platforms Kalshi and Polymarket has fallen 20% from its peak as the 2026 World Cup comes to an end.
Sharp Decline in Activity
Combined open interest (OI) on both platforms dropped from a peak of nearly $2 billion at the start of July to about $1.6 billion a few days before the final.
On a weekly basis, total open interest rose from $1.2 billion in late May to $1.8 billion in early July, before falling to around $1.5 billion by mid-July.
Volume Drop After World Cup Peak
Sports betting dominated both platforms during the tournament:
- Kalshi sports volume peaked at $9 billion in the week ending July 5, then dropped 55% to around $4 billion.
- Polymarket sports volume fell 70% from $2.3 billion to $740 million over the same period.
Sports betting made up roughly 80% of total volume on both platforms throughout the World Cup.
World Cup Final Result
Spain defeated Argentina 1-0 in the final on July 19, securing their second World Cup title.
Trader Performance on Polymarket
According to post-tournament data:
- 194,000 addresses traded the World Cup winner market
- Around two-thirds of traders lost money
- 54 addresses made over $100,000 (including 5 who earned more than $1 million)
- 43 addresses lost more than $100,000
Why the Drop Was Expected
The group stage featured many matches across 48 teams, creating hundreds of betting markets. As the tournament moved to knockout rounds, the number of daily matches decreased sharply, reducing betting opportunities. With the final now over, the main catalyst has disappeared.
Open interest fell more gradually than trading volume because outstanding bets only unwind when markets are resolved.
What’s Next?
Prediction market activity is expected to stay lower until the next big event — the U.S. midterm elections in the fall.
