Margin

The Regulatory Architecture — Three Layers

Three distinct regulatory authorities establish the margin requirements that govern brokerage accounts, each addressing a different dimension of the borrowing relationship.

The Federal Reserve Board established Regulation T — codified at 12 CFR Part 220 — under its authority in Section 7 of the Securities Exchange Act of 1934 to regulate credit extended by broker-dealers to their customers for securities purchases. Regulation T sets the initial margin requirement — the minimum percentage of a new purchase that the investor must fund from their own resources at the time of purchase.

For equity securities, Regulation T's initial margin requirement is fifty percent of the purchase price. An investor who wishes to buy ten thousand dollars of marginable stock must deposit at least five thousand dollars of their own funds — the broker may lend the remaining five thousand.

FINRA Rule 4210 establishes the maintenance margin requirements — the minimum equity percentage that must be maintained in a margin account after the initial purchase as the value of the securities fluctuates. As confirmed by FINRA's margin regulation resources, Rule 4210 requires that the margin maintained in all customer accounts be at least twenty-five percent of the current market value of all margin securities held long.

This is the regulatory floor — most broker-dealers impose stricter house maintenance requirements of thirty to forty percent, and they may do so at their discretion.

Individual broker-dealer house rules may impose requirements stricter than both Regulation T and FINRA Rule 4210 at any time — they can require higher initial margin percentages, higher maintenance percentages, or both for specific securities, concentrated positions, or volatile market conditions. House rules may never be more permissive than the regulatory minimums — a broker may not lend more than fifty percent of the purchase price even if the investor requests it.

Minimum Account Equity — The $2,000 Floor

Before any margin borrowing can occur, FINRA Rule 4210 requires that the account contain a minimum equity of two thousand dollars.

This minimum applies to the initial opening of a margin account and must be maintained at all times.

An investor with less than two thousand dollars in equity cannot open or maintain a margin account regardless of what percentage of their portfolio is their own funds. Some broker-dealers impose higher minimum equity requirements than two thousand dollars — this is a permissible house rule stricter than the FINRA floor.

The Initial Margin Calculation — Regulation T

When an investor places a margin buy order, the calculation proceeds as follows. The investor selects a purchase amount. Regulation T requires fifty percent of that amount to come from the investor's own equity. The broker lends the remaining fifty percent. The loan creates a debit balance in the account — the amount owed to the broker.

A concrete example: an investor wants to purchase twenty thousand dollars of marginable stock. Regulation T requires fifty percent — ten thousand dollars — from the investor's own funds. The broker lends the other ten thousand. The investor's equity is ten thousand dollars. The debit balance is ten thousand dollars.

The ratio of equity to total market value is fifty percent at the moment of purchase. As the securities value changes, this ratio changes — and if the value falls sufficiently, the maintenance margin requirement is breached.

The Maintenance Margin and the Margin Call

After the initial purchase, the ongoing obligation is the maintenance margin requirement — the minimum equity percentage that must be maintained continuously as the market value of the securities fluctuates.

Using the standard regulatory minimum of twenty-five percent: the investor who purchased twenty thousand dollars of stock with ten thousand dollars of their own equity and ten thousand dollars borrowed has an account with twenty thousand dollars in market value and ten thousand dollars in equity, for an equity percentage of fifty percent — well above the twenty-five percent minimum.

If the stock price falls, the market value declines while the debit balance remains fixed — the broker is owed ten thousand dollars regardless of what the stock is worth. As the market value falls, the equity falls by the same dollar amount and the equity percentage declines.

The critical margin call trigger point — the market value at which the equity percentage falls to the maintenance requirement level — can be calculated precisely.

Margin call trigger equals debit balance divided by one minus the maintenance margin percentage.

With a ten thousand dollar debit balance and a twenty-five percent maintenance requirement: ten thousand divided by one minus twenty-five percent equals ten thousand divided by zero point seventy-five equals thirteen thousand three hundred and thirty-three dollars. If the market value of the position falls to thirteen thousand three hundred and thirty-three dollars, the equity is thirteen thousand three hundred and thirty-three minus ten thousand equalling three thousand three hundred and thirty-three dollars, which is exactly twenty-five percent of thirteen thousand three hundred and thirty-three dollars. Below this level, a margin call is triggered.

A margin call — specifically a maintenance margin call or a FINRA Rule 4210 call — demands that the investor restore the equity in the account to at least the maintenance margin level by depositing additional cash, transferring in additional marginable securities, or selling securities in the account to reduce the debit balance.

A Regulation T call — sometimes called a Fed call — is triggered when a new purchase exceeds the available margin in the account, requiring the investor to deposit the required initial margin within the payment period. Under Regulation T, the payment period is three business days from the trade date.

Broker Rights in a Margin Account — The Key Examination Point

One of the most important and frequently tested facts about margin accounts is the scope of the broker-dealer's rights when a margin call is not met.

Under most margin agreements and under the applicable regulatory framework, the broker-dealer may liquidate securities in the margin account without prior notice to the investor and without waiting for the investor to respond to a margin call.

The SEC's investor bulletin on margin accounts confirms this directly: a broker may be able to sell securities at any time without consulting the customer first, and under most margin agreements the firm can do this even if the firm offers to give the investor time to increase equity. The investor has no right to choose which securities are liquidated — the broker makes that determination.

This forced liquidation right protects the broker's interest in the collateral but can be devastating to the investor, particularly during market downturns when the same conditions that triggered the margin call may also produce poor liquidation prices.

Short Selling and Margin Accounts

Short selling — the practice of selling securities that the investor does not own, borrowing them from the broker with the intention of repurchasing them at a lower price to return to the lender — requires a margin account. Regulation T prohibits short selling in a cash account.

For short positions, the margin requirements are structured differently from long positions. An investor who short sells must deposit initial margin equal to the full proceeds of the short sale plus an additional fifty percent of the current market value as required by Regulation T — meaning the short seller must deposit one hundred and fifty percent of the short sale proceeds as collateral. FINRA Rule 4210 specifies the maintenance requirement for short positions as the greater of five dollars per share or thirty percent of the current market value for stocks priced at five dollars or above.

The risk of a short position is theoretically unlimited because a stock can rise indefinitely, requiring the short seller to repurchase at any price. This unlimited upside risk is the reason short selling requires a margin account — the broker needs the collateral protection of margin requirements when the investor's potential loss is not capped.

Pattern Day Traders — Replaced by the Intraday Margin Standard

Until June 4, 2026, FINRA Rule 4210 classified an investor as a pattern day trader if they executed four or more day trades — buying and selling the same security on the same day — within any five business day period, provided those day trades represented more than six percent of the investor's total trading activity in the account during that period. Amendments filed as SR-FINRA-2025-017 and approved by the SEC on April 14, 2026 eliminated that designation with effect from June 4, 2026, replacing the day trading margin requirements in their entirety with an intraday margin standard.

The requirements that followed from the designation went with it: the minimum equity of twenty-five thousand dollars that a pattern day trader had to maintain in its margin account at all times, the day trading buying power that let a pattern day trader trade up to four times its maintenance margin excess, and the restrictions that applied when a pattern day trader's equity fell below that minimum. The two thousand dollar minimum equity for margin accounts generally is unaffected. Under the intraday margin standard, which applies to customer margin accounts other than good faith and portfolio margin accounts whatever the customer's trading frequency, the member firm determines the intraday margin deficit, if any, that the day's transactions create in the account — whether by monitoring in real time and blocking transactions that would create or increase a deficit, or by a single calculation of the deficit as it does for maintenance margin — and requires any deficit to be satisfied as promptly as possible. Member firms that need more time may phase in the new standard until October 20, 2027, and may continue to apply the former day trading margin requirements in the meantime.

The intraday margin standard addresses the heightened risk profile of day trading by measuring the exposure itself rather than counting trades — round-trip transactions within a day can create substantial intraday exposure that a maintenance requirement computed on the positions held at the close of the day does not capture, since a position opened and closed within the day leaves nothing at the close for that calculation to measure.

Securities Eligible and Ineligible for Margin

Not all securities can be purchased on margin. Regulation T specifies which securities are eligible for margin lending — generally, exchange-listed equities and certain OTC equities meeting Federal Reserve criteria are marginable. Several important categories are not eligible for margin.

Initial public offerings cannot be purchased on margin during the restricted period following the offering — the investor must pay the full purchase price in a cash account. Mutual fund shares newly purchased cannot serve as collateral for margin borrowing until held for thirty days — during which time they must be fully paid for. Non-marginable securities — including most penny stocks and other securities determined by the broker to be too volatile or illiquid for margin — require one hundred percent cash payment regardless of account type. United States Treasury securities, government agency securities, and municipal bonds operate under different margin rules under Regulation T — exempt securities — and broker-dealers set margin requirements for these in good faith, typically at substantially lower percentages than the fifty percent required for equities.

The Leverage Amplification Effect

Margin trading amplifies both gains and losses. An investor who purchases ten thousand dollars of stock using five thousand of their own funds and five thousand borrowed has two-to-one leverage. A ten percent rise in the stock price produces a ten percent gain on the total position — a one thousand dollar gain — but on the investor's five thousand dollar equity, that represents a twenty percent return. The leverage doubles the equity return when the position moves favourably.

The same leverage doubles the loss when the position moves adversely. A ten percent decline in the stock produces a one thousand dollar loss on the ten thousand dollar position — a twenty percent loss on the five thousand dollar equity.

Sufficiently large declines can not only eliminate the investor's equity entirely but produce a loss exceeding the initial equity investment — the investor can owe the broker more than they originally deposited if the position drops dramatically before a margin call can be satisfied.

The SEC's investor bulletin on margin accounts explicitly warns that investors can lose more than the amount of money initially invested in a margin account — a critical risk that distinguishes margin accounts from cash accounts where losses are always limited to the amount invested.

Examination Relevance and Key Takeaways

Margin is tested on the SIE and Series 7 examinations in the context of account types, leverage, the regulatory framework, margin call calculations, and the broker's rights to liquidate margin positions.

The key points to retain are these.

Margin is borrowing from a broker-dealer to purchase securities, amplifying both gains and losses. Three regulatory layers govern margin: Regulation T — issued by the Federal Reserve under 12 CFR Part 220 pursuant to Securities Exchange Act Section 7 — sets the fifty percent initial margin requirement for new equity purchases; FINRA Rule 4210 sets the twenty-five percent minimum maintenance margin requirement for long positions; and individual broker-dealer house rules may impose stricter requirements than either regulatory minimum but may never be more permissive.

The minimum account equity to open or maintain a margin account under FINRA Rule 4210 is two thousand dollars.

The Regulation T initial margin requires fifty percent of the purchase price from the investor's own funds — the broker lends the remaining fifty percent, creating a debit balance.

The maintenance margin call trigger equals the debit balance divided by one minus the maintenance margin percentage — at this market value, equity has declined to exactly the maintenance requirement. The broker-dealer may liquidate margin account positions without notice and without waiting for the investor to respond to a margin call — the investor cannot choose which positions are sold.

Short selling requires a margin account — cash accounts may not be used for short sales. The pattern day trader requirements — the designation of those executing four or more day trades within five business days comprising more than six percent of total trading, and the twenty-five thousand dollars minimum equity that followed from it — were eliminated from FINRA Rule 4210 effective June 4, 2026 and replaced by an intraday margin standard under which the firm determines each margin account's intraday margin deficit and requires it to be satisfied as promptly as possible, firms that need more time being permitted to phase it in until October 20, 2027. IPOs, newly purchased mutual fund shares within thirty days, and non-marginable securities require one hundred percent cash payment. Margin losses can exceed the initial equity investment — investors can owe more than they deposited.