Margin Trading

Margin trading is borrowing from a brokerage to buy securities, with the portfolio itself pledged as collateral. Regulation T, the Federal Reserve rule governing credit, lets an investor borrow up to 50% of the purchase price of eligible securities: $5,000 of cash controls $10,000 of stock. The broker charges interest on the loan daily, and FINRA and the exchanges set a minimum maintenance requirement of 25% equity, though most brokers set house requirements of 30% to 40%.

The leverage cuts both ways and not symmetrically in practice. A 2-for-1 leveraged position that falls 20% has lost 40% of the investor's equity, and a further decline triggers a margin call, a demand to deposit cash or sell positions at whatever the market is offering. Forced liquidation requires no notice the investor can act on. Retirement accounts cannot use margin, which makes margin trading by definition a taxable-account activity, with the interest generally nondeductible against wages.

The account runs on an equity ledger. Opening a margin position, the investor's cash and the broker's loan together buy the securities, and equity is the market value of the holdings minus the loan balance. Regulation T sets the initial requirement at 50%, so $10,000 of cash buys $20,000 of stock with $10,000 borrowed. The broker charges interest on the borrowed balance daily, at rates that have run from roughly 6% to 13% a year depending on the broker and the balance, and the interest accrues against equity whether the position wins or loses.

The maintenance requirement is where the risk lives. Equity must stay above the maintenance level, 25% of market value by the FINRA minimum and higher at most brokers. A $20,000 position on $10,000 of equity falls 25% to $15,000; equity is $5,000, which is 33% of market value, still above a 30% house requirement. At a 40% fall, the position is $12,000 and equity is $2,000, or 16.7%, and the margin call arrives: deposit cash or watch the broker sell.

The liquidation is the part investors do not feel until it happens. A margin call can be met by deposit or by the broker's forced sale, which requires no consent, happens at prevailing prices, and closes the positions the broker chooses rather than the ones the investor chooses. Concentrated and volatile positions carry higher house requirements, and a portfolio with no diversification at 2-to-1 leverage is a single bad week from liquidation. The 1929 crash ran on 90% margin, and the arithmetic that forced the selling spiral has not changed since.

Margin matters because it converts market volatility into forced decisions. An unleveraged investor in a 30% drawdown can hold, rebalance, or do nothing; the same drawdown at 2-to-1 leverage is a 60% equity loss and a margin call that sells at the trough whether the investor has decided anything or not. The interest compounds daily against a portfolio that must not merely win but win by more than the rate, which makes margin a race the market does not always let you finish.

I watched a colleague named Brent (yes, that Brent) borrow against a concentrated tech portfolio in late 2021 to buy more of the same portfolio, describing the loan as free money at 2%. The 2022 drawdown met his 2022 margin call, and the broker's liquidation executed at prices he would never have chosen. The leverage doubled the position on the way up and doubled the selling on the way down.

The highest-leverage thing most Americans can do is invest unleveraged: the historical equity premium was earned without borrowing, and the same compounding arrives without a liquidation clause. Investors who use margin anyway should size the borrowing for the worst historical drawdown, not the average year. Size the position with the position size calculator and stress the drawdown with the drawdown risk calculator.