Interactive Brokers' Path to Doubling: Growth Already Outpacing Requirements

Interactive Brokers shares are trading around $89, which puts them roughly 10% below their 52-week peak. The stock doesn't come cheap—investors are paying about 29 times what the company is expected to earn next year, a valuation you'd typically see attached to a growth stock, not a brokerage. The question worth asking is whether that premium makes sense, and whether the business can grow into it.

For the stock to double by the end of 2031, it would need to climb about 15% per year. That's a straightforward math problem with two moving parts: how much the company actually earns, and what multiple investors will attach to those earnings. The second part is beyond anyone's control. The first part is where the story gets interesting.

If Interactive Brokers can double its earnings per share over the next five years while the valuation multiple stays where it is now, the stock doubles. The company is already well on its way. In the first half of 2026, net interest income—the money earned from client cash balances and margin loans—grew 20% year over year. Commission revenue climbed about 25%. Earnings per share jumped 30%. These are not modest numbers. But here's the constraint: the company already converts roughly 77% of its net revenues into pre-tax profit. There's almost no room left to squeeze margins tighter. So earnings growth will track revenue growth almost exactly. And revenue depends on two things: how much money clients keep with the broker, and how actively they trade.

The balances tell the real story. Net interest income was $2.8 billion in 2023, $3.1 billion in 2024, and $3.6 billion in 2025—more than half of last year's total revenue. What's striking is that this growth hasn't needed the Federal Reserve's help. The Fed cut rates three times in the second half of 2025, yet growth actually accelerated, from 13% the year before to 20% in the first half of 2026. Customer balances were rising faster than rates were falling. At the end of August, customers held $185.6 billion in credit balances and had taken $101.5 billion in margin loans—both up sharply, 27% and 41% respectively, from a year earlier. For net interest income to double by 2031 with rates unchanged, those balances would need to roughly double as well, reaching around $370 billion and $200 billion. Interest rate moves still matter—a quarter-point shift in Fed policy would swing annual net interest income by roughly $81 million, or about 2% of the current line. But margin loans are the wild card. They hit $108.5 billion in the second quarter before falling to $101.5 billion by August. A severe market downturn could shrink them far faster than any gradual climb.

Balances follow customers, and customers keep arriving. Interactive Brokers ended August with 5.46 million client accounts, 35% more than a year before. The average account holds about $176,000 in equity. If that average stays flat, doubling the balances means doubling the accounts to roughly 11 million. That requires 15% annual growth. The company is currently growing at 35%. Even if growth slowed by more than half, the math still works. An ugly bear market could stall things for a year or two, but the requirement leaves room for that kind of disruption.

The real uncertainty sits elsewhere. Charles Schwab trades at roughly 13 times forward earnings. Interactive Brokers trades at more than double that—29 times. If earnings double over five years but the valuation multiple compresses from 29 to 20, the stock returns roughly 38% total, or about 7% annually. If the multiple holds steady at 29, the same earnings double sends the stock up 100%. The business itself—the part that shows up in the monthly numbers—is already doing the heavy lifting. Whether investors will still pay a premium for it in 2031 is the question no one can answer.