SkarpChapter 20 of 27
Margin Accounts and Short Selling Fundamentals
Examine how borrowing in a margin account amplifies gains and losses, how short sales work, and what regulations and risks govern these leveraged strategies.
Big Picture: Why Margin and Short Selling Matter
Why This Topic Matters
Margin and short selling add borrowing and leverage on top of the accounts and orders you already know. They are high-yield topics on the SIE and central to active trading.
Margin Account Definition
A margin account is a customer account in which a broker-dealer lends the customer part of the purchase price of securities, using the account’s assets as collateral.
Leverage and Short Selling
Leverage means using borrowed funds to control a larger position, magnifying gains and losses. Short selling means selling borrowed securities, hoping to buy them back cheaper.
Key Rule Sources
Regulation T sets initial margin. FINRA and exchanges set maintenance. SEC rules govern short sales, including the short sale price test restriction (alternative uptick rule).
Your Learning Goals
You will learn to compare cash vs margin accounts, compute basic margin requirements, and explain how short sales work and why their risk can be very high.
Cash Accounts vs Margin Accounts
Cash Account Basics
In a cash account, the customer must pay the full purchase price for securities by settlement. No borrowing from the broker-dealer is allowed.
Margin Account Basics
In a margin account, the broker-dealer lends part of the purchase price. Securities and other assets in the account secure this loan as collateral.
Who Uses Which?
Cash accounts suit buy-and-hold or retirement investors. Margin accounts suit active traders and investors who want leverage or to short sell.
What Requires Margin?
Short stock positions and many options strategies must be in a margin account. You cannot short stock in a cash account.
Risk Contrast
Cash account long stock loss is limited to what you paid. Margin adds interest costs, margin calls, and the risk of forced liquidation by the firm.
Structure of a Margin Account: Long vs Short
Account Building Blocks
Margin accounts show market value (MV), a debit or credit balance, and equity (EQ). Equity is the customer’s true ownership interest in the account.
Long Margin Formula
In a long margin account, equity equals market value minus the debit balance: EQ = MV - DR. The debit balance is what the customer owes the firm.
Short Margin Formula
In a short margin account, equity equals the credit balance minus market value: EQ = CR - MV. The credit balance includes short sale proceeds and margin.
Numerical Long Example
Buy $10,000 of stock, deposit $5,000, borrow $5,000. MV = $10,000, DR = $5,000, so EQ = $5,000. The position is 50% equity, 50% debt.
Numerical Short Example
Short $10,000 of stock, deposit $5,000. CR = $15,000, MV = $10,000, so EQ = $5,000. Again, equity is 50% of the position’s value.
Initial Margin Requirements: Reg T and Firm Rules
What Is Initial Margin?
Initial margin is the amount a customer must deposit when opening a new margin position. It must be met before or at settlement.
Reg T 50% Rule
Regulation T generally requires 50% initial margin for most stock purchases and short sales in a margin account. The firm can lend the remaining 50%.
Numerical Illustration
Buying or shorting $10,000 of marginable stock usually requires a $5,000 customer deposit, with $5,000 financed by the broker-dealer.
Other Requirements
FINRA and exchanges set minimum equity rules. Firms can impose stricter "house" margin requirements than Reg T, especially for volatile securities.
Non-Marginable Securities
Some securities, like many new issues or penny stocks, are not marginable. They must be fully paid even if held in a margin account.
Worked Examples: Long Margin Calculations
Scenario Setup
Customer buys 200 shares at $50 in a margin account. Purchase value is $10,000. Reg T at 50% means the customer must deposit $5,000.
Account After Purchase
MV = $10,000, DR = $5,000, EQ = $5,000. The position is 50% equity and 50% debt, matching the Reg T initial margin rule.
Price Rises to $70
MV becomes $14,000. DR stays $5,000. EQ = $9,000, so equity percentage is about 64.3%. A $4,000 gain on a $5,000 investment is an 80% return.
Price Falls to $35
MV falls to $7,000. DR is still $5,000. EQ = $2,000, equity percentage about 28.6%. A 30% price drop caused a 60% equity loss.
Takeaway on Leverage
Margin amplifies both gains and losses. The same price movement creates a bigger percentage impact on the customer’s equity than in a fully paid cash account.
Maintenance Margin and Margin Calls
What Is Maintenance Margin?
Maintenance margin is the minimum equity that must be kept in a margin account after a position is opened. Falling below it triggers a margin call.
Typical Minimums
FINRA minimums often tested: 25% of market value for long stock, 30% for short stock. Firms can set stricter house maintenance percentages.
Checking Maintenance
If MV is $7,000 and DR is $5,000, EQ is $2,000. Required at 25% is $1,750. Because $2,000 > $1,750, no margin call is triggered.
Finding Trigger Price
For a long account, set MV - DR = Maintenance% × MV. Solve for MV to find the price at which equity falls to the minimum allowed.
Numerical Trigger Example
With DR = $5,000 and 25% maintenance: MV - 5,000 = 0.25 MV, so 0.75 MV = 5,000, MV ≈ $6,667. Below this, a margin call occurs.
Short Selling Mechanics in a Margin Account
Short Sale Definition
In a short sale, the investor borrows shares, sells them in the market, and later buys them back to return to the lender, hoping the price falls.
Why Margin Is Required
Short stock must be in a margin account because the investor is borrowing securities. The account holds sale proceeds plus margin as collateral.
Account Flow
Short sale proceeds and the customer’s margin deposit create a credit balance. The account also shows a short position at the sale price.
Regulation SHO and Locates
Before shorting, the broker-dealer must reasonably believe shares can be borrowed, known as a locate, under SEC Regulation SHO.
Price Test Restriction
If a stock falls 10% from yesterday’s close, SEC Rule 201 restricts new shorts: they generally cannot be done at or below the national best bid.
Worked Examples: Short Margin and Unlimited Risk
Opening the Short
Short 200 shares at $50. Proceeds are $10,000. Reg T margin is $5,000, so CR = $15,000, MV = $10,000, EQ = $5,000.
Price Falls to $35
MV falls to $7,000, CR stays $15,000, so EQ rises to $8,000. The short seller would profit $3,000 if they bought back now.
Price Rises to $80
MV rises to $16,000, CR is $15,000, so EQ would be negative. In practice, the firm issues a margin call before equity hits zero.
Unlimited Risk
Because a stock’s price can rise without limit, a short stock position has theoretically unlimited loss potential. This is a key SIE test point.
Compare to Long Stock
Long stock risk is limited to what you paid. Short stock risk is unlimited on the upside. Remember this contrast for exam questions on risk profiles.
Risks, Disclosures, and Firm Powers in Margin Accounts
Leverage and Margin Calls
Leverage amplifies losses. If equity falls below maintenance, the firm issues a margin call. Failure to meet it can lead to forced liquidation.
Firm’s Right to Liquidate
Under the margin agreement, the broker-dealer can sell securities in the account without the customer’s consent to satisfy margin requirements.
Costs of Margin
Customers pay interest on borrowed funds and may pay extra fees for borrowing hard-to-borrow stocks, especially in active short selling.
Short-Specific Risks
Short sellers face unlimited loss potential, short squeezes, buy-ins if shares are recalled, and must pay any dividends on borrowed shares.
Disclosures and Suitability
Firms must provide margin risk disclosures and obtain signed agreements. KYC and suitability rules still apply when recommending margin strategies.
Thought Exercise: Comparing Cash vs Margin Outcomes
Scenario Setup
Investor A buys 100 shares at $40 in a cash account. Investor B buys the same in a margin account, investing $2,000 and borrowing $2,000.
Three Price Outcomes
Consider future prices of $20, $40, and $60. For each, find the position value for both investors and B’s equity (MV minus the $2,000 loan).
Compare Returns
Calculate percentage gains or losses for A and B. Notice how B’s leveraged position magnifies both upside and downside moves.
Margin Call Reflection
With a 25% maintenance requirement, at what market value does B’s equity fall to 25% of MV? Use EQ = MV - 2,000 and set EQ = 0.25 MV.
Takeaway
Use this exercise to internalize how margin changes risk. This intuition helps you answer SIE questions about leverage, margin calls, and suitability.
Check Understanding: Account Types and Eligibility
Test your understanding of which transactions require margin and how accounts differ.
Which of the following transactions MUST be executed in a margin account rather than a cash account?
- Buying common stock and paying in full on settlement
- Purchasing a new issue of common stock in an IPO
- Selling common stock short
- Buying shares of a marginable stock and holding them fully paid
Show Answer
Answer: C) Selling common stock short
Short sales of stock must be done in a margin account because the investor is borrowing securities to sell. Buying stock and paying in full can be done in a cash account. New issues are not marginable when first issued and must be fully paid.
Check Understanding: Margin Calculations and Risk
Apply formulas for equity and maintenance margin.
A customer buys $20,000 of marginable stock in a long margin account. Reg T is 50%, and the customer deposits exactly the required amount. Later, the stock’s market value falls to $14,000. If the maintenance requirement is 25%, which statement is TRUE?
- The account is below maintenance and a margin call will be issued.
- The account’s equity is $4,000, which is above the maintenance requirement.
- The debit balance is $10,000 and the equity is $4,000.
- The customer must deposit $1,500 to meet the maintenance requirement.
Show Answer
Answer: B) The account’s equity is $4,000, which is above the maintenance requirement.
Initial purchase: MV = $20,000; Reg T deposit = $10,000; DR = $10,000; EQ = $10,000. After MV falls to $14,000, DR is still $10,000, so EQ = $14,000 - $10,000 = $4,000. Maintenance at 25% requires 0.25 × $14,000 = $3,500. Actual equity ($4,000) is above $3,500, so the account meets maintenance. The debit balance is $10,000, not $?; the required deposit is $0.
Key Term Review: Margin and Short Selling
Flip through these cards to reinforce core terms and formulas you will see on the SIE.
- margin account
- A customer account in which a broker-dealer lends the customer a portion of the purchase price of securities, with the securities and other assets in the account serving as collateral, subject to initial and maintenance margin requirements.
- Initial margin (Reg T for most stocks)
- The amount a customer must deposit when opening a margin position. Under Regulation T for most equity securities, it is 50% of the purchase or short sale amount, though firms may require more.
- Maintenance margin (long stock)
- The minimum equity that must be maintained in a long margin account after a position is established. FINRA’s minimum for most long stock positions is 25% of the current market value, though firms may set higher house requirements.
- Equity formula: long margin account
- EQ = MV - DR, where MV is the market value of securities and DR is the debit balance (amount owed to the broker-dealer).
- Equity formula: short margin account
- EQ = CR - MV, where CR is the credit balance (short sale proceeds plus margin) and MV is the current market value of the securities sold short.
- Short sale
- A transaction in which an investor borrows securities and sells them in the market, intending to buy them back later at a lower price to return to the lender.
- Short sale price test restriction (SEC Rule 201)
- A rule that, when a stock declines 10% or more from the prior day’s close, restricts new short sales in that stock so they generally cannot be executed at or below the current national best bid for the remainder of that day and the next day.
- Unlimited loss potential
- A risk profile where losses are not capped. A short stock position has unlimited loss potential because a stock’s price can rise without limit.
- Margin call
- A demand from the broker-dealer that the customer deposit additional cash or securities when equity in a margin account falls below required levels (initial or maintenance).
- House margin requirement
- A margin requirement set by a broker-dealer that is stricter than regulatory minimums, often used for volatile or low-priced securities.
Key Terms
- buy-in
- An action taken by a broker-dealer to purchase securities in the market to cover a customer’s short position when borrowed shares are recalled or cannot be delivered.
- leverage
- The use of borrowed funds to increase the size of an investment position, which amplifies both potential gains and potential losses.
- short sale
- A transaction in which an investor borrows securities and sells them, intending to buy them back later at a lower price to return to the lender.
- margin call
- A demand by a broker-dealer that a customer deposit additional funds or securities because the equity in a margin account has fallen below required levels.
- cash account
- A brokerage account in which the customer must pay the full purchase price for securities by the settlement date and may not borrow from the broker-dealer.
- short squeeze
- A rapid increase in a stock’s price that forces short sellers to buy shares to cover positions, which can drive the price even higher.
- initial margin
- The amount a customer must deposit when opening a margin position before or at settlement, commonly 50% of the purchase or short sale amount for most stocks under Regulation T.
- margin account
- A customer account in which a broker-dealer lends the customer a portion of the purchase price of securities, with the securities and other assets in the account serving as collateral, subject to initial and maintenance margin requirements.
- debit balance (DR)
- In a long margin account, the amount the customer owes the broker-dealer for securities purchased on credit.
- maintenance margin
- The minimum equity that must be maintained in a margin account after the position is established; falling below this level triggers a margin call.
- credit balance (CR)
- In a short margin account, the sum of the short sale proceeds and the customer’s margin deposit held by the broker-dealer as collateral.
- Regulation T (Reg T)
- Federal Reserve Board regulation that governs the extension of credit by broker-dealers for securities transactions, including setting initial margin requirements for most equity trades.
- house margin requirement
- A firm-specific margin requirement that is stricter than regulatory minimums, applied at the discretion of the broker-dealer.
- short sale price test restriction (SEC Rule 201)
- An SEC rule that, when triggered by a 10% intraday decline from the previous close, restricts new short sales in that security from being executed at or below the current national best bid.