Margin and leverage: how borrowing amplifies gains and losses

Leverage means using borrowed money, or instruments that behave like borrowed money, to take a larger position than your own cash would allow. Margin is the most common form for stock investors. It makes good outcomes look better and bad outcomes much worse, and it adds a risk that does not exist with plain ownership: you can be forced to sell at the worst possible time.

How margin works

A margin account lets you borrow from your broker using the securities in the account as collateral. You pay interest on the borrowed amount at a rate set by the broker, which varies by firm and by balance size.

Three terms matter:

• Initial margin. Under the Federal Reserve's Regulation T, you can generally borrow up to 50% of the purchase price of eligible securities, so you need to fund at least half yourself.
• Maintenance margin. After the purchase, your equity must stay above a minimum percentage of the position's market value. FINRA sets a floor of 25%, and brokers frequently require more, such as 30% or higher, and can raise it for volatile or concentrated holdings, sometimes without notice.
• Margin call. If your equity falls below the maintenance requirement, the broker demands that you add cash or securities or reduce the position. Brokers can sell your holdings, and choose which to sell, without waiting for your agreement.

Leverage          = Position value / Your equity
Equity percentage = (Position value - Loan) / Position value
Margin call level = Loan / (1 - Maintenance requirement)

Not every security is marginable. Some low-priced or newly listed stocks are excluded, so check your broker's list.

Example (illustrative numbers)

You have $10,000 of your own money and borrow $10,000 to buy $20,000 of stock. That is 2x leverage. Interest is ignored for the moment.

The gains and the losses are both doubled. Now add the maintenance rule. If your broker requires 30% equity, the margin call level is $10,000 / (1 - 0.30), about $14,286. That is a drop of roughly 28.6% from $20,000. At $14,000 in the table, your equity is $4,000, or about 28.6% of the position, which is below the requirement. You would receive a call, or the broker could start selling.

Interest also counts against you. At a hypothetical 8% annual rate, the $10,000 loan costs $800 a year. The $20,000 position has to gain about 4% over the year ($800) just to cover the interest before you profit from using margin.

Why the downside is worse than it looks

• Forced selling locks in losses. Margin calls arrive when prices are already down. If the market recovers later, a position that was sold on the way down does not recover with it.
• Losses can exceed your deposit. In a sharp fall or overnight gap, the position can lose more than your equity, and you owe the broker the shortfall.
• Recovery math is harsher. Losing 40% of your capital requires about a 67% gain to get back to even.
• Interest is a fixed cost. It accrues whether the stock rises, falls or goes sideways.

Other forms of leverage

Margin is not the only route. Options and futures carry built-in leverage, because a small amount of money controls a large exposure. See options basics and futures basics. Leveraged exchange-traded funds aim to deliver a multiple of an index's daily return and reset each day, so their results over longer periods can differ substantially from simply multiplying the index's long-term return. Short selling also relies on margin, which is covered in short selling.

Companies use leverage too, in the form of debt, with similar logic: borrowing can raise returns to owners when things go well and increase the risk of distress when they do not. See debt-to-equity ratio.

How to think about it: rules of thumb

• Treat leverage as a risk multiplier, not an edge. It does not make a stock a better investment, only a larger bet.
• Measure the position against the worst plausible decline, not the average one. Drawdown data shows how deep declines have been.
• Leave a large buffer between your equity and the maintenance level, since both prices and broker requirements can change quickly.
• Match leverage to your temperament and time horizon. See risk tolerance and time horizon.

Common mistakes

• Using the maximum borrowing available.
• Ignoring the maintenance level until a call arrives.
• Forgetting that a rate shown today may change.
• Using margin to concentrate in a single stock.

Key takeaways

• Margin lets you borrow against your portfolio, typically up to 50% of a purchase at the start, with a lower ongoing maintenance requirement.
• Leverage multiplies both gains and losses, and interest raises the break-even.
• A margin call can force sales at low prices, and losses can exceed what you deposited.
• Position size, buffer and time horizon matter more once leverage is involved.