Up 18% Already in 2026, Is it Too Late to Buy Interactive Brokers Stock?

Interactive Brokers (NASDAQ: IBKR) just closed the books on a very impressive 2025, featuring rapid growth across a number of important metrics.

Highlighting its momentum, the online brokerage company added over 1 million net new accounts in 2025. And, for the full year, client equity climbed 37% year over year to $780 billion. That's a $200 billion year-over-year increase.

In short, the growth stock continues to live up to its premium valuation, but with shares up about 18% already in 2026, is it too late to buy the stock? After all, this sharp gain is on top of an approximately 46% increase in 2025. And the stock's performance is even more astounding when you zoom out. Over the past five years, shares have risen more than 340%.

So, are shares still a buy?

Image source: Getty Images.

Interactive Brokers continues to impress

Shares of Interactive Brokers rose about 5% on Wednesday morning, following its fourth-quarter earnings release on Tuesday afternoon. The quarterly results showed another period of strong growth, reminding investors of how Interactive Brokers has become a compounding machine.

The company's fourth-quarter revenue rose 21% year over year. This was fueled by a 22% year-over-year increase in commission revenue and a 20% boost to its net interest income.

Net interest income remains the most important driver of Interactive Brokers' business, accounting for $966 million of its $1.64 billion in revenue during the period. But commission revenue is still an important driver, accounting for $582 million of Interactive Brokers' total revenue.

Supporting its commission revenue growth during the quarter was a combination of strong growth in customer accounts and trading activity. The company saw 27%, 22%, and 16% year-over-year growth in customer trading volume in options, futures, and stocks, respectively. And Interactive Brokers maintained its healthy growth rates in customer accounts during the quarter; customer accounts rose 32% year over year, to 4.4 million.

All of this led to an impressive 27% year-over-year increase in non-generally accepted accounting principles (GAAP) earnings per share.

"In the fourth quarter, we continue to demonstrate the power and leverage of our diversified, fully automated global platform," explained Interactive Brokers' director of investor relations during the company's fourth-quarter earnings call.

Is Interactive Brokers still a buy?

Looking at these financial results, it's clear that Interactive Brokers' underlying business is doing extremely well. But price matters. Has the stock gotten ahead of itself?

As of this writing, the stock commands a price-to-earnings ratio of 34. On the surface, this seems fair for a company growing as fast as Interactive Brokers is. However, a closer look reveals two reasons to be cautious.

First, given that Interactive Brokers' business is closely tied to market activity, a market drawdown could lead to lower customer activity and slower customer account growth. If this were to happen, investors could get spooked, and shares could sell off.

Second, Interactive Brokers' significant reliance on net interest income means that if interest rates decline significantly, the company could face difficult comparisons, and its net interest income growth could slow or even turn negative, dragging on overall results.

However, even with these risks considered, I think Interactive Brokers' shares remain attractive. This is because the company's surging account growth suggests it is gaining significant market share. And continued strong account growth, I believe, could help offset potential headwinds from declining interest rates or a potentially more pessimistic market environment.

This brings us to the most important words in Interactive Brokers' fourth-quarter update. When Interactive Brokers founder and chairman Thomas Peterffy was asked during the company's fourth-quarter earnings call whether he sees account growth slowing down, he was adamant: "No. That is my answer. No."

"I do not see any reason why our account growth would slow down," the chairman added. "It will continue at the rate that we have been going. You see, the benefit that we have is our platform is attractive to many people."

With durable momentum in customer account growth like this, I think Interactive Brokers remains an attractive stock today, even after its big run-up in 2025 and early 2026. But given the business's ties to broader market sentiment and the stock's premium valuation, this is a high-risk stock. So, investors should keep in mind that there are no guarantees. Additionally, given the risks the company and the stock face, keeping any position in the stock small is probably a good idea.

Daniel Sparks and his clients have no position in any of the stocks mentioned. The Motley Fool has positions in and recommends Interactive Brokers Group. The Motley Fool recommends the following options: long January 2027 $43.75 calls on Interactive Brokers Group and short January 2027 $46.25 calls on Interactive Brokers Group. The Motley Fool has a disclosure policy.