Short Margin Account Calculations
Now that you understand long margin accounts, short accounts follow the same logic in reverse. Where long accounts use debit balances, short accounts use credit balances. Where long accounts profit from rising prices, short accounts profit from falling prices.
Key Terms and Formulas
| Term | Definition | Formula |
|---|---|---|
| Short Market Value (SMV) | Current market value of securities sold short | Price x Shares |
| Credit Balance (CR) | Total funds in the account (sale proceeds + customer deposit) | Fixed once established |
| Equity | Customer's ownership stake | CR - SMV |
| Regulation T (Reg T) Requirement | Total of 150% of SMV (100% proceeds + 50% deposit) | SMV x 150% |
The key formula: Equity = CR - SMV (compare to long: Equity = LMV - DR)
Initial Short Sale Example
A customer sells short 100 shares of ABC at $50/share:
- Short sale proceeds: $5,000
- Reg T deposit (50% of SMV): $2,500
- Credit balance: $7,500 (proceeds + deposit)
- Short market value (SMV): $5,000
- Equity (CR - SMV): $2,500
The credit balance is $7,500, consisting of the $5,000 sale proceeds plus the $2,500 Reg T deposit. The credit balance is fixed (like the debit balance in a long account); it does not change with market fluctuations. The 150% Reg T requirement ($7,500) equals the credit balance at inception.
Exam Tip: Gotchas
- The credit balance is locked in at the time of the short sale. Unlike market value, which fluctuates daily, the credit balance never changes. This mirrors how the debit balance (DR) is fixed in a long margin account.
- Reg T for short sales requires a 150% credit balance (100% proceeds + 50% deposit). At inception, the credit balance always equals exactly 150% of SMV.
Price Decline (Favorable for Short Seller)
If ABC falls to $40/share:
- Credit balance: $7,500 (unchanged)
- SMV: $4,000
- Equity (CR - SMV): $3,500
- Reg T requirement (50% of $4,000): $2,000
- Excess equity: $1,500
The short seller profits when the stock price falls because equity increases. Excess equity can be used for additional short selling. Selling power equals 2 x SMA (Special Memorandum Account).
Think of it this way: You sold something at $50 hoping to buy it back cheaper. When the price drops to $40, your potential profit grows, and your equity in the account reflects that gain.
Exam Tip: Gotchas
- Short seller equity moves opposite to the stock price. Price down = equity up. This is the reverse of a long account where price down = equity down.
Price Increase (Unfavorable for Short Seller)
If ABC rises to $60/share:
- Credit balance: $7,500 (unchanged)
- SMV: $6,000
- Equity (CR - SMV): $1,500
- Reg T requirement (50% of $6,000): $3,000
- Account status: Restricted (equity < Reg T)
Rising prices erode a short seller's equity. The account becomes restricted when equity falls below the Reg T requirement, but no maintenance call is issued unless equity drops below 30% of SMV.
Exam Tip: Gotchas
- A restricted short account is not the same as a maintenance call. The account is restricted (no new short sales without depositing more), but the broker does not force liquidation until equity falls below 30% of SMV.
Long vs. Short Account Comparison
| Feature | Long Account | Short Account |
|---|---|---|
| Fixed value | Debit balance (DR) | Credit balance (CR) |
| Variable value | Long market value (LMV) | Short market value (SMV) |
| Equity formula | LMV - DR | CR - SMV |
| Profit when | Price rises | Price falls |
| Maintenance minimum | 25% of LMV | 30% of SMV |
| Buying/selling power | 2 x SMA | 2 x SMA |
Exam Tip: Gotchas
- Short maintenance (30%) is higher than long maintenance (25%). Short selling carries unlimited risk (no cap on how high a stock can go), so regulators require a larger equity cushion.
- The exam tests whether you can apply the right formula. Long equity = LMV - DR; Short equity = CR - SMV. Mixing them up produces the wrong answer on every calculation question.