What it means
A margin account lets an investor borrow from a broker, using assets in the account as collateral, to fund part of a securities purchase. The investor’s own stake is called equity. The borrowed amount is a debt: it remains payable even if the securities fall in value. Broker interest, fees and margin requirements also affect the result.
Margin trading creates leverage. A percentage change in the investment’s value can produce a larger percentage change in the investor’s equity. Losses can exceed the initial cash contributed, and the broker may sell securities to protect its loan under the account agreement. Broker requirements and applicable rules vary.
How it is calculated
For a simple purchase with one outstanding loan and no other account assets or liabilities, calculate equity and the equity ratio as follows:
Equity (US$) = current position value (US$) − outstanding loan (US$)
Equity ratio (%) = equity (US$) ÷ current position value (US$) × 100
Current position value is the market value of the purchased securities. Outstanding loan is the amount still owed to the broker; if interest has been added to the loan balance, include it. Equity is the remaining value attributable to the investor before other costs. The equity ratio expresses that stake as a percentage of the position’s current value; it is not a measure of profit.
At purchase, a simple measure of leverage is Initial leverage (×) = purchase value (US$) ÷ investor cash contributed (US$). This assumes the cash contribution is the investor’s entire initial equity in the position. Broker interest and trading costs are separate from these simplified calculations.
Worked example
Suppose, hypothetically, an investor contributes US$5,000 and borrows US$5,000 to purchase US$10,000 of stock. Initial leverage is US$10,000 ÷ US$5,000 = 2×, and the initial equity ratio is 50%.
- If the stock rises 10%: The position becomes worth US$11,000. With the loan unchanged at US$5,000, equity is US$6,000: a US$1,000 gain, or 20% of the investor’s US$5,000 contribution before interest and costs.
- If the stock falls 10%: The position becomes worth US$9,000. Equity is US$4,000: a US$1,000 loss, or 20% of the initial contribution before interest and costs. The equity ratio is US$4,000 ÷ US$9,000 × 100 ≈ 44.4%.
A larger decline could trigger a margin call or liquidation, depending on the broker’s requirements. These examples are illustrations, not outcomes or thresholds for any particular account.
Why it matters before you trade
A pre-trade check should distinguish the stock’s risk from the financing risk. A position that appears affordable with borrowed funds can still leave the investor exposed to interest, changing collateral values and a requirement to add funds or reduce the position. Check the broker’s initial and maintenance margin requirements, interest terms and liquidation rights; the broker may act without waiting for the investor to respond to a margin call.
Also consider whether a price gap or an illiquid market could prevent an orderly exit. Selling at an unfavorable price may leave a balance owed after the position is closed. Position value, equity and available cash are different figures and should not be treated as interchangeable.
How PreTrAIde uses it
PreTrAIde’s stated quantitative measures include liquidity, volatility, estimated spread, market impact and 1-day 95% value at risk; they do not include a margin calculation or a check of broker-specific borrowing requirements. Its pre-trade analysis assesses a proposed stock basket before an order is placed and returns decision-support verdicts, risk assessments and reasoning. Those outputs do not establish whether a margin account can support the trade. PreTrAIde is not a broker and never places an order.
Common mistakes
- Treating borrowing capacity as cash: Borrowed funds must be repaid, with applicable interest.
- Comparing only dollar gains and losses: Leverage changes gains and losses as a percentage of the investor’s equity.
- Assuming a margin call guarantees time to respond: A broker’s agreement may permit liquidation without advance notice.
- Ignoring costs and gaps: Interest, execution costs and abrupt price moves can worsen the result shown by a simplified example.