Can I Lose More Money Than I Put Into My Account?

A stock can go to zero. It cannot go lower.

That single fact decides the answer. If you buy shares with your own settled cash, the worst outcome is that the company fails and the shares become worthless, so your loss is capped at what you paid, and nothing about the trade can create a bill afterward. Everything that breaks the cap involves borrowing something: money, shares, or the obligation that comes with selling an option.

Three ways an account goes below zero

Margin. You borrow part of the purchase price from the broker. Under the Federal Reserve’s Regulation T, the initial requirement for most stock purchases is 50%, so you can buy about twice what your cash alone would buy. FINRA then sets a maintenance minimum of 25% equity, and many brokers set their own higher house levels on top of it, and once your equity drops below whichever level applies you get a margin call, which the broker can meet by selling your positions without waiting for you. If the price falls so far that the position is worth less than the loan, the shortfall is yours.

Short selling. You sell borrowed shares and must buy them back later. A long position can only fall to zero. A short position has no ceiling on the loss, because there is no ceiling on how high a stock can go.

Selling options. Writing an uncovered call carries the same open-ended risk as a short sale, and writing puts can cost far more than the premium collected. Buying options is different. There, the premium is the most you can lose.

A margin gap, worked through

The danger is speed. Maintenance calls assume the broker can sell you out before equity runs out, and a price that jumps overnight on bad news skips every level in between.

No margin call could have helped. At the FINRA 25% minimum, the call would have come at about 33.33 on this position, but the stock never traded there, since it went from 50 at the close to 20 at the open without printing a single price in between.

A short squeeze, worked through

Short positions fail in the other direction. Say you have 8,000 of equity and short 200 shares at 30, collecting 6,000. A buyout offer at 75 is announced before the open, and the stock opens near the offer price.

The loss was one and a half times the amount you received for selling the shares. That happens with nothing exotic, since a short can lose several times its starting value whenever the price more than doubles, and takeover bids, surprise approvals and crowded squeezes are exactly the events that do it in one step. Hard-to-borrow names add fees and recall risk on top.

How to cap the loss

Start with the account type. A cash account that only buys stock cannot go below zero from trading, which is the main case made in starting in a cash account.

Then size positions to the gap. A stop feels like a cap. It is a trigger, and what happens to your stop when a stock gaps explains why the fill can land far past it. On margin, ask a harder question: if this stock opened 60% lower tomorrow, would the account still be positive?

Use defined-risk structures when you want leverage or a bearish view:

• A long put in place of a short sale.
• A long call in place of margin.
• Spreads with a bought leg.

Each has a maximum loss you can calculate before you enter. Options behave differently from stock in several other ways, covered in options are a different trade.

Finally, read your buying power figure as a limit set by the broker, not a recommendation. It tells you what the broker will lend.