Margin, Leverage and Forced Exit

Week 8 · Borrowed capital shortens the distance to a forced closure

Course lens

How can a small retail trading account survive execution friction, drawdowns, leverage, and increasingly complex instruments?

The question this week answers

When the account controls more exposure than it can fully fund, how small can an adverse price move be before the broker takes control?

The point is not to find a “best” trading style or instrument. It is to understand what can make the account fail.

By the end of this lecture

  1. explain how a margin loan works on an ordinary stock position
  2. explain why a short position’s risk profile differs from a long position’s
  3. describe leverage as a multiplier applied to both gains and losses
  4. calculate the price at which a simulated margin account triggers a margin call

Borrowing changes the account, not the stock

Margin

Borrowing part of a position’s cost, using account equity as collateral.

Leverage

Total position size divided by the trader’s own capital in it.

Short selling

Borrow, sell, buy back later — the loss has no theoretical ceiling.

Margin call

Forced action once equity falls below the broker’s maintenance requirement.

Leverage doesn’t just magnify losses — it shortens how much adverse movement the account can survive before a broker closes the position for it

A worked example

A simulated $10,000 stock position, split $5,000 trader capital and $5,000 margin loan (2x leverage), against a 25% maintenance margin requirement. The loan stays fixed while equity shrinks as the position falls — the position doesn’t need to reach zero for the account to be in trouble.

The numbers: a margin call trigger

equity = position value − $5,000 loan


margin call when equity = 25% × position value



position − 5,000 = 0.25 × position


0.75 × position = 5,000 → position = $6,666.67

$6,666.67 ÷ $10,000 = 66.7% of the original value — a 33.3% price drop triggers this call, well before the position is worth zero. The exact threshold depends on the broker’s own rules; the example isolates the leverage mechanism.

Long vs. short, side by side

Long position

Max gain: unlimited. Max loss: 100% — price can’t go below zero.

Short position

Max gain: 100% — price can’t go below zero. Max loss: unlimited.

Short selling — borrow shares, sell them, buy them back later. Profits if price falls; the loss has no ceiling if it rises instead.

The numbers: an uncapped short loss

Simulated short, 100 shares at $20

Price doubles to $40 → buy-back costs $4,000 → $2,000 loss (100% of proceeds)

Price triples to $60 → buy-back costs $6,000 → $4,000 loss (200% of proceeds)

There is no price at which the loss stops growing — unlike a long position bought outright.

More leverage means less room for error

No leverage · 1x

Price has to fall 100%, to zero, to wipe out the position.

Stock margin · 2x

33.3% to a margin call, using this week’s simulated example.

Futures-like · 10x

Small moves in the underlying dominate the posted margin.

Try it yourself

Calculate

A simulated $20,000 position, bought with $8,000 own money and $12,000 margin, against a 30% maintenance margin requirement.

Calculate the price level, as a percentage of the original position value, at which a margin call triggers.

The takeaway

  1. Leverage multiplies both gains and losses relative to the trader’s own capital.
  2. A margin call is the mechanical consequence of leverage, not an edge case.
  3. A short position’s loss has no ceiling, unlike a long position’s 100% cap.
  4. Weeks 9 through 11 keep this same forced-exit logic, just embedded in different instruments and venues.

Next week

Week 9 — futures as a case study in embedded leverage and forced liquidation, before options’ more complex payoff structure.