In August, clients of Interactive Brokers traded 3% less than they had in July. In the same month, the balances those clients kept at the firm grew by $56 billion . Which of those two facts deserves more weight is, very nearly, the entire argument over the stock.
The company reports a single operating segment, brokerage . There is no conglomerate structure to unpick and no underperforming division to spin out. What there is instead is one franchise with two revenue engines of unequal size, which the market habitually treats as one. In the second quarter of 2026, reported on July 21, commissions contributed $673 million of $1.90 billion in net revenue, up 30% year over year, while net interest income contributed $1.06 billion, up 23% . Market-data fees, exchange-mandated order-flow payments, risk-exposure charges and investment gains made up the modest remainder. Roughly two-thirds of net revenue is earned in the United States, the rest through subsidiaries operating in 39 countries and territories . Pretax margin was 77%, on reported and adjusted figures alike .
One structural feature distorts every screen and is worth clearing up first. Interactive Brokers is an umbrella-partnership structure: consolidated pretax income of $1,456 million in the quarter left just $312 million of net income available to common stockholders, or $0.69 diluted on 450.1 million shares, with $1,026 million attributed to noncontrolling interests . The listed company owns roughly a quarter of the operating LLC; founder-controlled Holdings owns the rest. A headline market capitalization near $157 billion therefore measures the whole as-converted structure — it implies about 1.73 billion shares at the current price — while the listed stub is closer to $41 billion (450.1M diluted shares × $90.69 ).
The August giveback priced the one line that slowed
Through late August the stock was among the better performers in financials, running 68% from a 52-week low of $58.95 to a high of $98.75. It closed at $90.69 on September 18, about 8% below that peak .
Nothing broke. What arrived was the monthly operating data. Daily average revenue trades fell 16% in July and a further 3% in August, with year-over-year growth decelerating from 27% to 23% . The dollar volume behind those trades fell harder: client trade money in U.S. Reg-NMS stocks — the total spent or received including commissions and fees — dropped from $820.0 billion in June to $614.5 billion in August, a 25% decline over two months . Against a second-quarter run rate of 4.8 million daily trades , the July–August average of roughly 4.35 million reads as a plain sequential slowdown.
Two things happened at once, which is why the tape is hard to read: the trade count visibly rolled over, and the Federal Reserve delivered a rate increase in the same week that pushed the broader rate-sensitive complex around. I do not think the hike explains the giveback, because for this business it is not a negative. What the monthly data did was hand a crowded, richly valued stock the first clean evidence of deceleration in the metric everyone watches. The metric everyone watches is the smaller engine.
Accounts and balances rose in the months trading fell
Interactive Brokers ended August with 5.460 million client accounts, 35% more than a year earlier and 3% more than in July, on client equity of $962.8 billion, also up 35% . Account growth in August was marginally faster than the 34% recorded in July . Client margin loan balances stood at $101.5 billion, 41% higher than a year earlier, and client credit balances — the uninvested cash that funds the interest engine — reached $185.6 billion, up 27% .
Those are not merely encouraging headline figures; they set the base for the quarter now ending. The second quarter earned its $1.06 billion of net interest income on average customer margin loans of $96.6 billion and average customer credit balances of $171.7 billion . August's ending balances sit above both. The interest-earning base going into the September quarter-end is therefore larger than the base that produced the record quarter the market has already applauded, even though clients were trading less while it grew.
The mechanism is simple enough to be overlooked. A funded account arrives with idle cash that must be held in segregated deposits and securities, and with a margin facility attached. It earns for Interactive Brokers whether or not the holder trades that day. Trade counts are a monthly mood indicator; balances are the annuity.
Net interest grew 23% into a 70 basis-point rate decline. Now it doesn't have to
The most underappreciated line in the second-quarter filing is the net interest margin table. Average interest-earning assets grew 37% to $228.6 billion, yet net interest margin fell to 1.93% from 2.07% . Every yield component moved against the firm: margin loans earned 4.10% versus 4.67% a year earlier, segregated cash 3.32% versus 3.86% . The average federal funds rate was 70 basis points lower year over year, and net interest income still rose 23%, with margin-loan interest up 39% on the strength of higher balances .
Put a number on what that cost. Fourteen basis points of lost margin, applied to the current $228.6 billion of average earning assets, is roughly $320 million of annualized net interest income forgone (0.14% × $228.6B ). That is the headwind the company has spent a year out-growing.
On September 16 the Federal Open Market Committee voted 12-0 to raise the target range a quarter point to 3.75%–4.00% , its first increase since 2023, with projections pointing to the possibility of another before year-end . The European Central Bank's benchmark stands at 2.5% and the Bank of Japan lifted its policy rate to 1.25% on September 18, a 31-year high . About a third of Interactive Brokers' interest-sensitive customer balances are denominated outside the dollar, and management's disclosed sensitivity is an $81 million change in annual net interest income per 25 basis points of federal funds, plus $38 million per 25 basis points across the relevant non-dollar benchmarks .
Be precise about the size of that. A synchronized 25 basis points across both buckets is roughly $119 million of annual pretax income. Applying the share of consolidated pretax that actually reached common stockholders last quarter ($312M ÷ $1,456M, or 21% ) across 450.1 million shares gives about six cents of attributable earnings — call it 2% of next year's consensus. The increment is not the point. The point is the sign. With portfolio duration held under 30 days , the repricing arrives in weeks rather than years, and the sensitivity was struck against June 30 balances that have since grown.
The fair objection is that a hawkish hike is not an unmixed blessing: it raises what clients pay to borrow, and margin loans are the most rate-elastic thing on this balance sheet. They did fall 7% in July . But they stabilized in August at a level 41% above the prior year , and the firm charges a spread over benchmark rather than a fixed rate, so a higher policy rate lifts the revenue on every dollar lent even as it modestly discourages the marginal borrower. The greater risk to balances is an equity drawdown, not the cost of carry.
A cost structure published monthly, to the basis point
Interactive Brokers discloses something almost no competitor does: the all-in cost of trading through it. In August, commissions and fees came to 0.008% of client trade money, and IBKR Pro clients' total cost of executing and clearing U.S. Reg-NMS stocks was about 2.1 basis points measured against a daily volume-weighted average price, versus 2.5 basis points over the trailing twelve months . That is the moat, quantified and updated every month.
It is sustained by headcount discipline bordering on the eccentric. Net revenue rose 28% while non-interest expenses rose 17%, leaving costs at 23% of net revenue against 25% a year earlier, with average employees up 6% to 3,249 . The result is a 77% pretax margin and a seventh consecutive quarter above 70% .
Because the cost base scales, new products are distribution rather than expenditure. On the July call management described becoming the first electronic broker to open access to both the Korea Exchange and Nextrade, launching IBKR Prediction Markets to route event contracts across ForecastEx, the CME and Kalshi to the best net price, and receiving preliminary conditional approval from the Office of the Comptroller of the Currency for a national trust bank charter it plans to have operational by year-end — the prerequisite for directly custodying mutual fund and ETF assets . In the two months since, it has added a white-label tie-up with Korea's Daol Investment & Securities , three programs in Japan including margin financing charged only on the amount actually borrowed , and an integration that lets U.S. users trade from a ticker page on X . Regulatory disruption elsewhere has helped too: management reported a clear increase in account and asset transfers after Chinese authorities clamped down on Tiger and Futu's mainland client acquisition . None of this involved paying up for customers, which is why the margin survives the expansion.
What breaks it: a reflexive loan book, an 81-year-old control block, and hurricane contracts
The bear case does not need account growth to stop. It needs the tape to turn, because in a drawdown every line moves the wrong way at once. A client base carrying $101.5 billion of borrowings is the most reflexive item on this balance sheet: falling collateral values shrink the loans, shrink the trading, and surface credit losses together. Customer bad debt expense in the first half was $11 million, $9 million higher than a year earlier, on losses tied to a single corporate action — small, but a reminder that this book is not risk-free. And commissions, at $2,149 million of $2,440 million of revenue from contracts with customers in 2025 , remain pure volume beta.
Governance is the standing reason this should not carry a top-of-band multiple. Thomas Peterffy, 81, controls approximately 73.7% of combined voting power through Holdings, which makes Interactive Brokers a controlled company exempt from Nasdaq's independent-majority requirements, and the compensation committee he chairs sets his own pay . There is no disclosed succession arrangement. Nor is there a buyback working in shareholders' favor: the only repurchases in the first half were $146 million of stock taken back for employee tax withholding under the incentive plans, against $150 million of treasury shares sold , and diluted shares rose to 450.1 million from 441.4 million over the year . The 10-K goes further, contemplating that redemptions of Holdings interests financed by share offerings could eventually add up to roughly 1,250.7 million shares against the 445.4 million then outstanding . Those offerings are the mechanism by which the founder's economic interest is converted into listed stock over time, and they are the reason per-share growth here must come entirely from earnings rather than from shrinking the count.
The newest product line carries the least-settled risk. The chairman has said the firm intends to concentrate on weather-related contracts and to bring in potential hurricane landfalls, acknowledging that this implies insurance risk . Event contracts on natural catastrophes sit precisely where commodities regulation meets state insurance law. The revenue is immaterial today; the headline risk is not symmetric with it.
Then there is the price itself. At 28.6 times forward earnings, a fade to 24 times on one soft quarter takes the stock to about $76 with nothing whatsoever wrong with the business.
At 28.6 times, the earnings have to do all the work
On consensus of $3.17 for 2027 across eight analysts, the stock trades at 28.6 times . Charles Schwab, at $105.25, trades at 13.4 times its 2027 consensus of $7.88; Robinhood, at $119.82, trades at 41.5 times $2.89 . Interactive Brokers sits in the middle of that spectrum, and the comparison flatters no one: its earnings per share represent a roughly one-quarter economic slice of the operating company, while Schwab's and Robinhood's are whole.
So the multiple is not the reason to own it. The reason is that the earnings line keeps coming in ahead of where the Street sets it. Second-quarter earnings of $0.69 landed 8% above the $0.64 mean of six analysts, and net revenue of $1.90 billion beat a $1.80 billion consensus ; the company has beaten its EPS consensus in at least six of its last eight reported quarters, including a strong streak of recent beats . More to the point, both variables that drive the September and December quarters — interest-earning balances and the benchmark rates applied to them — are currently running ahead of where those estimates were struck, while the variable that has visibly weakened is the smaller engine and is still growing 23% year over year.
My reading is that the market is marking Interactive Brokers on its trade count and underpricing its balance sheet. That is a defensible mistake heading into the October print and an increasingly hard one to keep making if the December quarter lands with a full quarter of higher benchmark rates behind it. The honest caveat is that at 28.6 times there is no cushion for a stumble, and a de-rate rather than an earnings miss is how an owner loses money here. But the earnings line is where consensus has been too low in each of a string of recent prints, and the rate cycle has just stopped working against it. Owning Interactive Brokers at this price is a bet on the earnings, not on the multiple — which, for this particular business, is the right side to be on.
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