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Financial Context Wiki

How Margin Accounts Work

For educational purposes only; not investment advice.

Direct answer

Section titled “Direct answer”

A margin account allows an eligible customer to borrow from a broker, using securities and cash in the account as collateral. Borrowing increases the market exposure supported by the customer’s own equity, so gains and losses relative to that equity are magnified.

The broker charges interest and controls the collateral under the margin agreement. If account equity falls below a requirement, the broker can demand more cash or securities, restrict activity, or sell positions. A customer may not receive advance notice or choose which assets are sold.

Equity and margin requirements

Section titled “Equity and margin requirements”

The basic account relationship is:

Account equity = current market value of securities - margin loan balance

Equity percentage = account equity / current market value of securities

An initial requirement determines how much equity is needed when a position is opened. A maintenance requirement determines the minimum equity that must remain afterward. US regulatory baselines and Federal Reserve rules can apply, but brokers may impose higher house requirements, change them without advance notice, and apply stricter terms to concentrated, volatile, low-priced, or illiquid securities.

Interest accrues on the debit balance even if the investment falls. Deposits, sales, dividends, fees, and settlement timing can change buying power and the loan balance. Margin buying power displayed by a broker is a ceiling under current assumptions, not a recommended position size or a guarantee that requirements will remain unchanged.

Leverage example

Section titled “Leverage example”

An investor contributes $5,000, borrows $5,000, and buys $10,000 of stock.

Position state Market value Loan Account equity Equity percentage
At purchase $10,000 $5,000 $5,000 50.0%
After a 20% decline $8,000 $5,000 $3,000 37.5%

The stock fell 20%, but account equity fell from $5,000 to $3,000, a 40% decline before interest and fees. Leverage amplified the percentage loss borne by the investor.

Suppose the broker’s maintenance requirement is 40%. At an $8,000 market value, required equity is $8,000 × 40% = $3,200; actual equity is $3,000, leaving a $200 deficiency. The broker’s remedy and deadline depend on its agreement and rules, and liquidation can create additional losses or taxes.

For a single position with loan balance L and maintenance rate m, the simplified market value at which equity equals the requirement is L / (1 - m). Real accounts can contain multiple positions, changing requirements, accrued interest, and other obligations, so broker calculations control.

Margin risks

Section titled “Margin risks”
  • Amplified losses: losses can exceed the cash initially deposited.
  • Forced liquidation: a broker may sell without waiting for the customer or a market recovery.
  • Requirement changes: higher house requirements can create a deficiency without another price move.
  • Interest drag: borrowing cost continues and rates can change.
  • Concentration risk: one volatile holding can reduce equity and buying power quickly.
  • Liquidity risk: forced sales in thin or stressed markets can receive poor prices.
  • Cross-position effects: one position’s loss can cause unrelated collateral to be sold.
  • Tax and strategy disruption: liquidation may realize gains or remove a hedge at an unfavorable time.

The broker’s right to protect its loan generally takes priority over the customer’s preferred holding period. Read the margin agreement and current security-specific requirements before relying on displayed buying power.

Common misconceptions

Section titled “Common misconceptions”

“A margin call guarantees time to deposit money.” The broker may liquidate immediately under the account agreement.

“Maintenance margin is always 25%.” Regulatory minimums are not universal broker terms; house and security-specific requirements can be higher.

“My maximum loss is my deposit.” A rapid decline, gap, interest, or liquidation deficit can produce losses beyond the initial cash contribution.

“Using only part of my buying power removes leverage risk.” Any borrowing introduces interest and collateral requirements; risk depends on exposure and buffer, not the label alone.

“A diversified account cannot receive a margin call.” Correlated declines, changing requirements, and cross-collateral effects can still create a deficiency.

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Authoritative sources

Section titled “Authoritative sources”