Executive Insight
The commission-equity ratio (CE ratio) is the primary quantitative metric used in securities litigation and FINRA arbitration to establish excessive trading. Defined as total account costs divided by average account equity over a measurement period, it measures the annualized drag that trading activity imposes on a client’s capital. This note formalizes the calculation methodology, reviews the legal thresholds established in case law, and provides calibration guidelines for compliance surveillance systems.
Core Framework
The CE ratio is computed as:
where $c_i$ is the cost of trade $i$ (commissions + spreads + margin interest), $E_t$ is end-of-month account equity, $T$ is the number of months, and $M$ is the measurement period in months (the $12/M$ factor annualizes). For options accounts, $c_i$ must include per-contract commissions, bid-ask spreads at execution, and assignment/exercise fees.
Legal thresholds from SEC enforcement actions and federal circuit opinions: CE > 6% is presumptively excessive (Mihara v. Dean Witter, 619 F.2d 814); CE > 12% is virtually conclusive (Costello v. Oppenheimer, 711 F.2d 1361). For options accounts, the effective thresholds are approximately 2× higher because bid-ask spreads and per-contract costs dominate. CE ratios of 20–40% are routinely documented in options churning cases.
Applied Example
An options account with average monthly equity of $185,000 generates $14,800 in monthly costs (commissions: $8,200; spreads: $4,100; margin: $2,500) over 11 months. CE = ($14,800 × 11) / $185,000 × (12/11) = 96%. At this level, the account must generate a gross annual return exceeding 100% merely to break even—an outcome achieved by virtually no institutional manager in history.
Implications
Compliance systems should flag any account with CE > 6% for review and escalate CE > 12% for mandatory investigation. The CE ratio is a necessary but not sufficient diagnostic; it should be combined with the turnover ratio and profit probability analysis for a complete forensic assessment. For litigation, the CE ratio provides the quantitative foundation on which expert testimony is built.
Derived from From Equations to Capital research program, by Mourad E. Mazouni, PhD, PMP. View Volume I →