What it means
A margin account can fund part of a stock purchase with money borrowed from a broker. The stocks serve as collateral, while the investor remains responsible for the loan. If the account’s equity falls below the broker’s maintenance requirement, the broker may issue a margin call.
Meeting a call may require adding cash or eligible securities, or reducing positions. The broker’s agreement determines the deadline and permitted responses. A broker may also liquidate holdings without waiting for the investor to respond; a margin call should not be treated as a guaranteed warning period. Requirements can vary by broker, security and account, and a broker can raise its own requirements.
How it is calculated
For a simple account holding one margined stock position, with no other balances or charges:
Equity (US$) = current stock value (US$) − outstanding margin loan (US$)
Equity percentage (%) = equity (US$) ÷ current stock value (US$) × 100
Maintenance deficiency (US$) = max[0, required maintenance equity (US$) − equity (US$)]
Required maintenance equity (US$) = maintenance margin rate × current stock value (US$)
The outstanding margin loan is the amount owed to the broker; this simplified calculation holds it constant as the stock price changes. The maintenance margin rate is the broker’s applicable minimum equity fraction, written as a decimal in the formula—for example, 30% is 0.30. Current stock value is the shares’ current market value. The deficiency measures how far equity is below the requirement at that value; it is not necessarily the amount of stock that must be sold.
This is an illustration, not a complete broker account calculation. Interest, fees, other positions and different requirements can change the result.
Worked example
Suppose, hypothetically, an investor buys 100 shares at US$100 each, for US$10,000 total. The investor contributes US$5,000 and borrows US$5,000 from a broker. Assume a 30% maintenance margin rate and ignore interest and fees.
- At purchase, equity is US$10,000 − US$5,000 = US$5,000, or 50% of the stock’s value.
- Suppose the shares fall to US$70 each. Their current value is 100 × US$70 = US$7,000. The loan remains US$5,000, so equity is US$2,000.
- Equity percentage is US$2,000 ÷ US$7,000 × 100 = approximately 28.6%, below 30%.
- Required maintenance equity is 0.30 × US$7,000 = US$2,100. The deficiency is US$100. If the broker permits a cash deposit and the stock value does not change, adding US$100 would bring equity to US$2,100.
A further price decline could create a larger deficiency. The broker’s actual notice and account rules govern what happens next.
Why it matters before you trade
Borrowing magnifies changes in account equity: a fall in the stock’s value reduces equity while the loan is still owed. A forced sale can occur at an unfavorable price and may leave a remaining loan balance. Checking the proposed position size, borrowing amount and broker’s maintenance rules helps make that exposure visible before an order is placed. A stop-loss order does not guarantee an exit price or prevent a margin call.
How PreTrAIde uses it
PreTrAIde does not state that it calculates margin requirements, monitors margin accounts or predicts margin calls. Its pre-trade analysis assesses a proposed stock basket before any order is placed, including risk, liquidity, volatility and estimated execution costs. Those checks can provide context for a leveraged position, but they do not replace the broker’s account-specific margin calculation. PreTrAIde’s GO, NO-GO and MODIFY verdicts are decision support, not recommendations; users place trades with their own broker.
Common mistakes
- Confusing initial and maintenance margin: The amount required to open a position can differ from the equity needed to keep it open.
- Assuming the deficiency is always the cash required: Broker rules and changing prices affect how a call can be met.
- Expecting a guaranteed deadline: A broker may liquidate collateral under its account agreement.
- Ignoring the loan after a sale: Liquidation does not necessarily erase every amount owed.