A margin call happens when the equity in your margin account falls below the broker’s maintenance margin requirement. The broker then asks you to deposit cash or securities, or to close positions, to bring the account back above that line. If you do nothing, the broker can liquidate positions on its own terms, without asking again.
That last part is what catches people out. A margin call is not a warning shot you can ignore. It is a deadline with a penalty attached, and the penalty is that someone else decides what gets sold and when. The math below shows exactly where that line sits and how a small price move can push you over it.
What maintenance margin actually is
When you buy securities on margin, you borrow part of the purchase price from your broker. The portion you fund yourself is your equity. Regulators set an initial margin floor (in the US, Regulation T currently requires at least 50% of the purchase price for new margin purchases), but the number that matters day to day is the maintenance margin.
Maintenance margin is the minimum equity your account must hold as a percentage of the position’s current market value. In the US, FINRA rules set a floor for most long stock positions, though many brokers require more. Brokers can raise requirements for volatile or concentrated positions, and they can do so without much notice. For short sales, the floor is typically higher, often around 30% or more.
Here is the key distinction: initial margin governs whether you can open the trade, whereas maintenance margin governs whether you can keep it open. A position can pass the first test easily, yet fail the second one after only a modest decline.
The margin call formula
Brokers calculate your equity as the market value of your positions minus the amount you borrowed. The maintenance requirement is the market value multiplied by the maintenance margin percentage. A margin call is triggered when equity drops below that requirement.
The threshold price, the point where equity equals the requirement, can be worked out directly. For a long position bought entirely with margin, the formula is:
Threshold price = loan amount / (shares × (1 − maintenance margin))
You do not need to memorize it. You need to understand what it implies: the threshold price is a function of how much you borrowed, how many shares you hold, and the maintenance percentage. Change any of those and the line moves.
Worked example: when the broker force-liquidates
Assume you buy 1,000 shares at $50, so the position is worth $50,000. You use $25,000 of your own cash and borrow $25,000, which satisfies the initial margin requirement, and your broker’s maintenance margin applies.
The maintenance requirement is 30% of the current market value, so at $50 that is $15,000. Your equity is $25,000, which means you have plenty of room.
Now suppose the stock falls to $40, making the position worth $40,000. You still owe $25,000, so your equity is $15,000, while the maintenance requirement is 30% of $40,000, which is $12,000. You are still above the line, but the buffer has shrunk from $10,000 to $3,000.
At $35, the position is worth approximately $35,000 and equity is around $10,000, yet the requirement may be about $10,500, so you could be below the line and the broker might issue a margin call. Using the threshold formula, the trigger price would be approximately $25,000 / (1,000 × 0.70), which suggests the call may arrive somewhere around that level, before the stock even reaches $35.
To cure the call at $35, you need equity of at least approximately $10,500. You appear to be short by around $500. You can deposit $500 in cash, or you can sell enough shares to reduce the loan. If you do neither, the broker can sell whatever it chooses. In practice, many brokers liquidate enough to restore the account to the maintenance level, and some sell more to rebuild a cushion. You do not get to pick the timing, and you may not get a phone call first.
Notice what drove the outcome: a 28.6% decline in the share price, from $50 to $35.71, wiped out 60% of your equity. That is leverage working in reverse, and the same amplification that makes gains look attractive makes drawdowns arrive faster than most people expect.
How the numbers shift with different assumptions
Change the maintenance margin to 40% and the threshold becomes approximately $41.67. The call now arrives after a decline of roughly 16.7%. A higher maintenance requirement does not change your loan, but it moves the trigger much closer to your entry price.
Change the leverage instead: if you had funded $40,000 yourself and borrowed only $10,000, the threshold at 30% maintenance would be approximately $14.29 based on typical margin formulas. The stock could potentially fall more than 70% before a call, because less borrowed money means more room—though also less upside per dollar invested.
This is the trade-off at the center of margin. There is no setting that gives you both high leverage and a wide safety buffer. The broker’s maintenance percentage and your loan size together determine how much adverse movement you can absorb.
What the broker can do, and what it cannot
Brokers are not required to give you time. Many will send a notice and allow a short window, often a few business days, to deposit funds or reduce the position. Others act immediately if the shortfall is large or the market is moving fast. During periods of high volatility, brokers frequently raise maintenance requirements on individual stocks, which can trigger calls across accounts that were previously comfortable.
You should also know that the broker is not obligated to sell the positions you would have chosen. It can liquidate anything in the account, and it can do so at whatever price the market offers. In a fast market, that price may be well below the level that triggered the call. The broker’s priority is protecting its loan, not optimizing your tax situation or your entry point.
One counter-argument is that margin calls are rare for diversified, conservatively sized positions, and that is true. An account holding broad funds with modest leverage and a cash buffer may never see one. However, margin requirements are set per position and per broker, so a concentrated bet in a single volatile stock can breach the line after a routine pullback. The risk is not evenly distributed.
Trader perspective (weeks to about six months)
If your holding period is short, the main risk is timing. A margin call can force you out of a position at the worst moment, before your thesis has time to play out. Short-term traders often use stop-loss orders to exit before the maintenance line is reached, which converts an uncontrolled liquidation into a planned exit. The trade-off is that stops can be triggered by intraday noise that a margin call might have survived.
Traders should also watch the broker’s maintenance requirements on the specific instrument. Leveraged ETFs, small-cap stocks, and options can carry requirements well above the standard 25% or 30%. A position that looks safe under the default assumption may not be.
Investor perspective (six months or longer)
If you are holding for the long term, margin calls are less about daily price swings and more about the interaction between leverage and drawdowns. A long-term investor using margin is effectively borrowing against future returns, so a severe market decline can force sales at depressed prices, locking in losses that would have recovered. Many long-term investors avoid margin entirely for this reason, or they keep leverage low enough that a 50% market decline would not trigger a call.
If you do use margin over a long horizon, the practical questions are how much you borrowed relative to your own capital, what the maintenance requirement is on each holding, and whether you have cash or liquid assets outside the margin account to meet a call without selling. Those three numbers determine your survival through a bad year.
Conclusion: the line is set before you trade
The maintenance margin threshold is not a mystery, because it is arithmetic: loan amount divided by shares times one minus the maintenance percentage. You can calculate it before you enter a trade and decide whether the implied cushion is acceptable. If a 20% decline in the underlying would trigger a call, you are running a leveraged position with a thin buffer, and the broker—not you—will choose the exit.
The practical takeaway is to know your broker’s maintenance requirement for each holding, keep your loan small relative to your equity, and hold cash outside the account if you want the option to meet a call on your own terms. Margin amplifies outcomes in both directions. The call is simply the point where the broker stops letting you decide which direction you are headed.
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Frequently Asked Questions
What is the difference between initial margin and maintenance margin?
Initial margin is the minimum equity required to open a margin position, currently at least 50% of the purchase price for US stock purchases under Regulation T. Maintenance margin is the minimum equity required to keep the position open, typically 25% to 30% or more depending on the broker and the security. A trade can satisfy the initial requirement and later fail the maintenance requirement after a price decline.
How long do I have to meet a margin call?
It depends on your broker and the size of the shortfall. Many brokers allow a few business days to deposit cash or sell positions, but they are not required to wait. If the market is moving quickly or the deficit is large, the broker can liquidate immediately without further notice.
Can a broker liquidate my positions without telling me?
Yes. The margin agreement you signed typically gives the broker the right to sell positions in your account to cover a shortfall. Many brokers send a notice as a courtesy, but they are not obligated to wait for your response before acting.
What happens if I cannot meet a margin call?
The broker will sell positions to bring the account back to the maintenance requirement. If the account still has a deficit after liquidation, you remain responsible for the shortfall and may owe the broker money. This is why margin debt can exceed the value of your remaining positions in a severe decline.
Does a margin call affect my credit score?
A margin call itself does not appear on your credit report. However, if you fail to cover the deficit and the broker sends the unpaid balance to collections, that can affect your credit. The immediate consequence is the forced sale of your positions, not a credit event.
AI Notice: This article was created wholly or predominantly with the assistance of artificial intelligence and was published without human editorial review.
This article is for general information only and does not constitute investment advice. Always do your own research before making trading decisions.