**Strong customer balance growth continues to underpin Interactive Brokers' net interest income heading into Q3 2026 results.** Record client equity, margin loans, and cash balances—reaching $182 billion in Q2—have offset pressure from lower benchmark rates, lifting Q2 NII 23% year-over-year to $1.06 billion. Each 25-basis-point rate shift affects roughly $81 million in annualized NII, making balance expansion the dominant variable. Recent account additions (34% YoY) and elevated trading volumes support further asset growth, though any slowdown in margin borrowing or shifts in the Fed's path could moderate momentum. Q3 earnings, due October 15, will clarify whether these trends persist into the quarter's close.