A margin call is the message every leveraged investor dreads: your broker says your account no longer has enough equity, and you need to add money or the broker will sell your stocks for you. It usually arrives after a sharp drop, which is exactly when selling is most expensive.
What Is Buying on Margin?
A margin account lets you borrow money from your broker, using the stocks you own as collateral. Under the Federal Reserve's Regulation T, you can generally borrow up to 50% of the purchase price of eligible stocks. That means $10,000 of your own cash can control $20,000 of shares.
Borrowing amplifies results in both directions. A 20% gain on the $20,000 position is a 40% gain on your $10,000. A 20% loss is a 40% loss on your $10,000, and you still owe the loan plus interest.
What Is a Margin Call?
Brokers must keep your account above a minimum equity level, called the maintenance margin. FINRA sets the floor at 25% of the securities' market value, and many brokers require more, often 30% to 40% for volatile or concentrated holdings.
Account equity is the market value of your securities minus the loan. When prices fall, the loan stays the same, so equity shrinks faster than the stock does. When equity as a share of market value drops below the maintenance requirement, the broker issues a margin call.
The Exact Price Drop That Triggers a Call
Assume you buy a stock using 50% of your own cash and 50% borrowed. The loan is half the original value. The call triggers when:
Equity ÷ Market value = Maintenance requirement
Solving for the price drop gives: Drop = 1 − 0.50 ÷ (1 − maintenance %).
| Maintenance requirement | Price drop that triggers a call | Example: $20,000 position falls to |
|---|---|---|
| 25% | 33.3% | $13,333 |
| 30% | 28.6% | $14,286 |
| 35% | 23.1% | $15,385 |
| 40% | 16.7% | $16,667 |
| 50% | 0% | $20,000 |
The loan is $10,000 in each row. These are arithmetic results for a simple long-only purchase, not a forecast for any stock. A broker's actual rules can be stricter, and they can raise requirements on a specific stock at any time.
The pattern is the point. The higher the maintenance requirement, the smaller the cushion. At a 40% requirement, an ordinary correction of 17% is enough. The VIX and a stock's beta both hint at how quickly that cushion can disappear.
What Happens When You Get the Call
You usually have three choices:
- Deposit cash to restore equity.
- Deposit other eligible securities that count toward the requirement.
- Sell positions to reduce the loan.
Be careful about the timing. Your margin agreement typically allows the broker to sell your securities without asking you first and without choosing the positions you would prefer to sell. In a fast market, a broker can act before you have finished reading the notice. Forced selling also locks in the loss and can create a taxable event.
Why Margin Calls Cluster in Selloffs
Margin calls feed on themselves. A falling market triggers calls, calls force selling, selling pushes prices lower, and that triggers more calls across other accounts. This is one reason sharp drops can accelerate. Crowded, heavily borrowed positions are the most exposed. The same mechanism works in reverse for people who are short: a rising price can force them to buy back shares, which is part of how a short squeeze builds. See also the short selling guide.
Costs Beyond the Call Itself
- Interest. You pay interest on the loan whether the stock rises or falls. Rates vary by broker and balance.
- Concentration risk. Borrowing to hold one stock multiplies the damage if that company has a bad earnings day or gaps lower. Read about gap risk before leveraging a single name.
- Losses can exceed your deposit. Unlike a cash account, a margin account can leave you owing money after positions are sold.
- Day trading rules. Margin accounts used for frequent trading may also fall under the pattern day trader rule.
How to Avoid a Margin Call
- Borrow well below the maximum. The 50% limit is a ceiling, not a target.
- Keep a cash buffer you could deposit within a day.
- Size positions for a big drop. Use position sizing so a bad week does not breach your requirement.
- Diversify. A call is calculated on the whole account, but one collapsing holding can drag it under. See concentration vs. diversification.
- Know your broker's actual requirement for each holding, not just the regulatory minimum.
- Plan your exit before you need it. A stop-loss set above the call level lets you sell by choice. Note that stop orders can fill below your price in a gap.
Using Price Alerts as an Early Warning
The best margin call is the one you never get. You can work backward from the table above:
- Find your broker's maintenance requirement and your loan balance.
- Calculate the price at which a call would trigger for each leveraged holding.
- Set a price alert at a level comfortably above that trigger, for example halfway between today's price and the call price.
- Set a second alert closer to the trigger as a final warning.
When the first alert fires, you can add cash, trim, or tighten a stop on your own schedule instead of reacting to a broker notice. Stock Alarm Pro sends price alerts to your phone, so you do not need to watch a screen. Steps are in How to Set Stock Price Alerts, and the same idea applies to volume spike alerts, which can flag heavy selling early.
The Bottom Line
Margin turns a normal drop into a forced decision. Know your loan, know your broker's maintenance requirement, calculate the price where a call would trigger, and put alerts well above it. If you cannot comfortably hold a position through a 30% decline, you probably should not borrow to own it.
This article is educational and is not investment advice. Margin rules differ by broker and can change, and margin trading carries a risk of losses greater than your deposit. Check your broker's margin agreement for the rules that apply to you.
