Kalshi and Polymarket combined open interest fell 20% from approximately $2 billion in early July to around $1.5 billion by the week ending July 19. The decline occurred days before Sunday's World Cup Final and followed the tournament's shift from a match-heavy group stage to narrower knockout rounds, which reduced available betting markets. Sports betting accounted for roughly 80% of total volumes on both platforms throughout the tournament, with Spain defeating Argentina 1-0 on Sunday to claim the country's second World Cup title.
Kalshi and Polymarket Sports Volume Declined Over 50% Through July 19
On a smoothed weekly basis, total open interest ran from $1.2 billion in late May to nearly $1.8 billion in the week ending July 5, then fell to around $1.5 billion by the week ending July 19. Kalshi's sports volume peaked at approximately $9 billion in the week ending July 5 and fell to around $4 billion by the week ending July 19, down about 55%. Polymarket's sports volume peaked near $2.3 billion and dropped to $740 million over the same span, down nearly 70%.
Polymarket World Cup Winner Market Saw 194,000 Addresses Trade
Profit and loss data compiled by DeFiOasis following the tournament's conclusion found that 194,000 addresses traded Polymarket's World Cup winner market, of which roughly two-thirds lost money. Most gains and losses were below $100. However, 54 addresses made more than $100,000 each—including five that cleared $1 million—while 43 lost more than $100,000 each.
Tournament Structure Drove Open Interest and Volume Fluctuations
The World Cup group stage that ran from mid to late June packed the schedule with matches across 48 teams, flooding both platforms with many markets to bet on. As the tournament bracket narrowed through the knockout rounds and the number of matches per day thinned out, the amount of markets people could bet on dried up. With the final played on July 19, the catalyst is now gone entirely. Open interest has fallen more gently than volume because volume is daily turnover, which collapses the moment there are fewer matches, while open interest is the outstanding stake that unwinds only as markets resolve.
FAQ
What caused Kalshi and Polymarket open interest to fall 20% in July?
The decline occurred as the World Cup progressed from a match-heavy group stage in mid-to-late June to narrower knockout rounds, reducing the number of betting markets available on both platforms. With the final played on July 19, the tournament catalyst ended entirely.
How many addresses traded Polymarket's World Cup winner market?
Profit and loss data compiled by DeFiOasis found that 194,000 addresses traded Polymarket's World Cup winner market, with roughly two-thirds losing money. Most gains and losses were below $100, though 54 addresses made more than $100,000 each and 43 lost more than $100,000 each.
How much did Kalshi and Polymarket sports volumes decline after the World Cup peak?
Kalshi's sports volume peaked at approximately $9 billion in the week ending July 5 and fell to around $4 billion by the week ending July 19, down about 55%. Polymarket's sports volume peaked near $2.3 billion and dropped to $740 million over the same span, down nearly 70%.
