Buying on margin means buying stock with money borrowed from your broker, using the stock itself as collateral. A margin call is what happens when the stock falls far enough that your collateral is no longer worth enough: the broker demands more cash immediately, and if you cannot pay, they sell your shares for you — at the worst possible moment.
You deposit $10,000. Your broker lets you borrow against it and buy, say, $20,000 of stock. You now control twice as much stock as you have money, so every 1% the stock moves is a 2% move in your equity. That is leverage, and on the way up it feels wonderful.
The broker is not doing this out of generosity. They hold your shares as collateral and require your own equity to stay above a minimum percentage of the position — the maintenance margin. If your equity falls below it, they issue a margin call.
Example (illustrative): you put in $10,000 of your own money, borrow $10,000, and buy $20,000 of a stock. Assume a 25% maintenance margin requirement.
The stock falls 25%. The position is now worth $15,000. You still owe the broker $10,000, so YOUR equity is $5,000 — you lost 50% of your money on a 25% decline. Your equity is now 33% of the position, still above the 25% line, so you are safe for now.
The stock falls further, to a total decline of 33%. The position is worth $13,333; you still owe $10,000; your equity is $3,333, which is exactly 25% of the position. One more tick down and you get the margin call. You must wire in cash within a day or two, or the broker liquidates. If you had bought the same stock with cash and no leverage, a 33% fall would be painful but survivable — you could simply hold and wait. On margin, you do not get to wait.
The forced sale happens at the bottom, by construction. Prices fall, margin calls fire, forced selling pushes prices down further, which triggers more margin calls. You are sold out at the point of maximum pessimism — precisely when a patient holder would be doing nothing. Worse, interest accrues on the borrowed money the whole time, so leverage has a running cost even in a flat market. This is why sober position sizing matters more than any forecast: a position that cannot survive a normal drawdown is a bad position no matter how good the thesis.
A margin call is not a judgement on your thesis — it is a mechanical consequence of the price path, and it can fire on a position that turns out to be right six months later. That is the deepest problem with leverage: it makes you vulnerable to the ROUTE the price takes, not just the destination. If you use margin at all, know your maintenance level and your invalidation level before you enter, and set a stop loss well above the point where the broker would act for you. None of this is investment advice.
The broker sells your positions — usually without warning and at whatever price the market offers — until your equity is back above the requirement. You do not choose what gets sold or when, and you remain liable for any shortfall.
Yes. Because you borrowed money, a sharp enough fall can leave the position worth less than the loan, and you still owe the difference. This is not possible when you buy stock with cash.
Experienced investors use modest leverage deliberately and size it so that a severe drawdown still does not trigger a call. The danger is not leverage existing — it is leverage large enough that a normal market decline forces you out of a position you would otherwise hold.
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Educational research only — not investment advice.