Interactive Brokers Is Holding $930 Billion of Customer Money. Here's What That Earns at Today's Rates.

Interactive Brokers (IBKR) now holds $930 billion in customer equity and is converting elevated interest rates into surging profitability. Net interest income jumped from $1.148 billion in 2021 to $3.56 billion in 2025, reflecting the broker's ability to earn on client cash balances in a higher-rate environment.

The platform added customers at a 34% year-over-year pace, reaching 5.19 million accounts. That growth underpins the expansion in assets under custody, though the real earnings driver remains the spread IBKR captures on uninvested cash.

Analysts at The Motley Fool warn that the stock's 37 price-to-earnings ratio prices in optimism that may not hold. The firm's net interest income is directly exposed to Federal Reserve policy, and any further cuts to the fed funds rate would compress the spread the broker earns on segregated client funds. Analysts recommend staying on the sidelines.