Kalshi and Polymarket Open Interest Falls 20% to $1.5B as World Cup Concludes

According to The Block, Kalshi and Polymarket combined open interest fell 20% to around $1.5 billion by the week ending July 19, following the conclusion of the World Cup on July 19. From a peak of approximately $2 billion at the beginning of July, the decline reflects the end of the tournament that had driven trading activity on both platforms.

Kalshi's sports volume dropped 55% from nearly $9 billion in the week ending July 5 to around $4 billion by July 19, while Polymarket's sports volume fell approximately 70% from a peak of $2.3 billion to $740 million over the same period. Sports markets accounted for roughly 80% of both platforms' total volumes throughout the tournament. The decline follows Spain's 1-0 victory over Argentina in the final, which marked the end of the major catalyst that had driven prediction market activity.