What it means
Margin means borrowing from a broker to buy investments, with the securities held as collateral. Under standard rule-based margin, each position needs a fixed deposit, such as 50% of its value for shares.
The rule is simple but ignores how positions offset each other. Portfolio margin looks at the portfolio as a whole.
The broker's system applies a set of stress scenarios, such as the market rising or falling by a set percentage and volatility shifting, and measures the worst loss across them. The margin required is based on that worst-case loss, subject to minimums.
The result is that a well-hedged portfolio, such as a long position in shares with offsetting short positions or options, needs far less margin than a concentrated, unhedged one. This frees up capital for the investor, who can then hold more positions or keep more cash.
The method rewards risk management. Portfolio margin is usually available only to experienced investors with a minimum amount of equity in the account.
Brokers must be approved to offer it, and they may apply their own, tighter requirements. Because it allows more leverage, losses can also be larger, and margin calls (demands to deposit more funds) can arrive quickly if markets move sharply.
For finance teams, the concept matters for treasury and trading desks, since lower margin requirements release cash but increase sensitivity to sudden market moves. A prudent approach holds a buffer above the minimum and stress tests the portfolio with scenarios worse than the broker's.
The rules differ between countries and brokers and can change, so investors should read the account agreement. The key point is that required margin is driven by the risk of the portfolio and can rise suddenly if volatility rises or hedges are removed.
In practice
Real-world examples.
Example
A hedge fund with offsetting long and short positions in the same sector qualifies for portfolio margin. Its required deposit falls sharply, and the manager uses the freed cash to add other positions. The risk team sets a limit so the fund never uses more than half the available margin.
Example
An individual investor with a large options position receives a margin call after a sudden market drop. The broker's stress test showed larger losses, which raised the requirement. The investor has to add funds or close positions within a day or two.
Example
A treasury desk holding a hedged bond portfolio uses portfolio margin to cut collateral needs. The desk keeps a cash buffer above the minimum in case volatility rises. It reviews the buffer every week and after any large market move.
Formula
Calculation
Portfolio margin requirement = worst-case loss across the stress scenarios
Suppose an investor holds $200,000 of shares and a $150,000 short position in a closely related index. A simple fixed rule of 50% on both sides would require 0.50 x (200,000 + 150,000) = $175,000.
Net exposure = 200,000 - 150,000 = $50,000. A 15% market move on this net exposure loses 0.15 x 50,000 = $7,500.
A residual mismatch risk of 4% on the hedged amount adds 0.04 x 150,000 = $6,000.
Worst-case loss = 7,500 + 6,000 = $13,500, so the portfolio margin requirement is about $13,500.
The reduction is 175,000 - 13,500 = $161,500, which shows why hedged investors favour the method, and why it carries risk if the hedge fails.Case study
Seen in the real world.
Cedar Point Investments is a fictional trading firm with $1,000,000 of equity. In this illustrative case, it moves from fixed-rule margin to portfolio margin on a hedged book of $2,000,000 long and $1,800,000 short positions. The fixed rule would require 50% of $3,800,000, which is $1,900,000, more than the firm's equity.
Under portfolio margin, the broker's scenarios show a worst-case loss of $240,000 on the hedged book. The firm can therefore hold the positions comfortably, with room to spare.
A few months later, a volatility spike widens the gap between the long and short legs, and the broker raises the requirement to $520,000. The firm had kept a large buffer, so it meets the increase without selling positions in a rush, and it records the episode as a reason to keep its buffer policy unchanged.
Watch out
Common mistakes.
- Assuming lower margin means lower risk. The risk is the same or higher, only the deposit is smaller.
- Running with no buffer. Requirements can rise quickly, and a forced sale can lock in losses.
- Believing hedges always work. If the offsetting positions stop moving together, the portfolio may lose more than the model expected.
Questions
People also ask.
Who can use portfolio margin?
Usually experienced investors with substantial account equity and a broker approved to offer it.
How is it different from standard margin?
Standard margin applies fixed percentages to each position, while portfolio margin measures the risk of the whole portfolio.
What is a margin call?
A demand from the broker to deposit more cash or securities because the account's equity has fallen below the required level, and a failure to respond can lead the broker to sell positions without asking.
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