Interactive Brokers Sits on $185.6 Billion in Client Cash as Anthropic’s IPO Approaches
Net interest income at Interactive Brokers hit $1.06 billion in the second quarter of 2026, according to The Motley Fool, rising 23% from a year earlier.
The growth came as uninvested client cash at the brokerage climbed to $182.4 billion by the end of June and grew further to $185.6 billion through the end of August.
Now a potential record-breaking IPO from AI company Anthropic could prompt clients to put a portion of that cash to work.
How Interactive Brokers Profits From Idle Cash
The mechanics are straightforward. Interactive Brokers is required by regulators to segregate customer cash, and it invests the bulk of those segregated funds in short-term U.S. government securities.
Clients receive interest on qualifying U.S. dollar balances, while the broker retains a spread of half a percentage point below the federal funds rate (the benchmark overnight lending rate set by the Federal Reserve).
At current scale, net interest income is the largest single revenue line for the firm. It accounted for more than half of the $1.9 billion in total net revenues the company reported for the second quarter of 2026.
Growth came from larger balances rather than wider margins.
The firm's net interest margin (the difference between what it earns on assets and what it pays to clients, expressed as a percentage) narrowed to 1.93% from 2.07% a year earlier as interest rates declined, yet net interest income climbed because total balances were higher.
Clients added roughly $39 billion in uninvested cash over the past year.
Commission revenue also set a record last quarter, reaching $673 million, up 30% year over year, helped in part by a 67% jump in customer margin loans (loans extended to clients who borrow against their investment holdings to buy more securities).
What Anthropic's IPO Could Mean for That Cash Pile
The Motley Fool reported, citing The Information, that Anthropic planned to file its IPO prospectus shortly after Labor Day, with a potential market listing as soon as late September 2026. No prospectus, share price, or share count has been made public.
Investor projections, as reported by CNBC, place Anthropic's valuation at around $2 trillion. The offering could exceed the current record, set by SpaceX (Nasdaq: SPCX), which raised $85.7 billion in its June 2026 debut.
Interactive Brokers navigated the SpaceX IPO directly. The company's head of investor relations, Nancy Stuebe, said the broker offered the SpaceX IPO to eligible retail clients in the United Kingdom and across multiple European countries.
The SpaceX IPO as a Benchmark
The SpaceX listing demonstrated both the opportunity and the effect of a mega-IPO on a broker like Interactive Brokers. Client cash that moves from idle balances into new shares reduces the pool the firm can invest for interest income.
At the same time, IPO activity drives commission revenue, margin borrowing, and new account openings.
The net effect on Interactive Brokers from a potential Anthropic offering depends on deal size, client participation rates, and how much cash clients choose to deploy. None of those figures are available yet. The cash pile continues to grow in the meantime.