Segregated margin is an incomplete exposure filter

A size bound is not a custody bound

Margin-management is a filter that keeps a loss or exposure decision bounded before entry and while a position is open, using account equity, volatility, stop distance, and exposure. Customer margin posted with a futures-commission-merchant is required to be held in accounts separated from the firm's own assets. That second requirement is about custody, not about how large the trade should be.

What segregation is meant to do

Segregation is intended so that a broker bankruptcy leaves client deposits and open positions transferable rather than absorbed by the insolvent firm. Comingling mixes client deposits with firm money and defeats the bankruptcy safeguard that segregation is meant to provide.

Why a reported surplus is not a bound

Brokers must report customer-segregated balances monthly, including the required amount and any excess or shortfall, but those published figures can be falsified. An apparent surplus of cash in a segregated account versus client balances is not a clean surplus because deposits, withdrawals, trades, and fees move constantly.

When the rules are not followed

Two brokerage failures showed that segregation rules protect clients only if firms follow them and overseers can verify them. After those failures, the industry self-regulator gained electronic access to broker bank accounts so segregated balances could be checked frequently. A deposit-insurance fund covering commodity traders was discussed as an added backstop against insolvency or a segregation breach.

Editorial reading

A trader who has already sized from equity, volatility, and stop distance still needs that second check. If customer-segregated-funds are not intact, the first-layer size no longer describes the cash that can actually absorb the loss. Frequent verification and an insurance backstop were discussed because the monthly published surplus cannot carry that load on its own.