Leverage does not create risk; it scales the risk already present in a financed portfolio and shortens the time available to respond to it. A portfolio that could tolerate an eighteen-month drawdown unlevered may have three weeks levered — not because the thesis changed, but because someone else now has the right to close the position.

This is a working framework for managing that constraint.

Start from survivable decline, not from target return

Most leverage decisions run backwards: an investor decides on a return objective and derives the exposure required. The durable approach inverts it.

Ask instead: what decline must this portfolio survive without forced action? For a diversified equity book, 35% is a reasonable planning assumption — it is roughly the drawdown of a normal cyclical bear market and well short of the worst on record.

Now derive the maximum loan. To remain above a 130% maintenance ratio after a 35% decline:

Required: (Collateral × 0.65) ÷ Loan ≥ 1.30
Therefore: Loan ≤ Collateral × 0.50

On a £500,000 portfolio, that is a £250,000 maximum — check the cost — even if the facility permits £350,000. The 100 basis points of extra return from drawing the additional £100,000 is not worth the loss of a third of your drawdown tolerance.

Position sizing under leverage

An unlevered investor sizing a position asks what it does to returns. A levered investor must ask what it does to the maintenance ratio.

Two rules cover most cases:

Cap single-name exposure at 10% of gross. Under leverage a 10% position in a stock that gaps 40% on a profit warning removes 4% of gross exposure in a morning — survivable. A 25% position removes 10% and can trigger a call on its own.

Size to the LTV, not the conviction. A high-conviction position in an illiquid mid-cap contributes far less borrowing capacity than its market value suggests. Sizing to conviction while the lender sizes to liquidity is how portfolios end up structurally over-levered without the investor noticing.

Correlation is the risk you actually carry

Diversification is measured in calm markets and tested in violent ones, and it does not survive the transition. In a sharp sell-off, cross-asset correlations converge toward one: sectors that behaved independently for years fall together, and the “diversified” book behaves as a single position.

Three practical adjustments:

  • Assume correlations of 0.8+ in stress when modelling drawdowns, regardless of historical averages.
  • Diversify across factors, not just names. Twenty positions that are all long-duration growth is one position held twenty times.
  • Treat geography and currency as separate axes. A UK-listed portfolio financed in sterling has a different risk profile from the same holdings financed in dollars.

Liquidity planning

Liquidity in a levered portfolio has two dimensions and both matter.

Portfolio liquidity — can you exit in a stressed market at a price close to the screen? Position size relative to average daily volume is the number to watch. A holding representing more than a day’s volume cannot be exited without moving the price against you, which is precisely when you will need to.

External liquidity — can you deposit funds within the response window? A margin call is only an emergency if you cannot meet it. Cash held outside the account, available within one business day and sized at roughly 10% of the loan balance, converts nearly every call into an administrative task.

The operational discipline

Frameworks fail on execution, not on design. Four habits carry most of the weight:

Monitor the ratio, not the P&L. Profit and loss tells you how you have done. The maintenance ratio tells you how much time you have. Only one of them can force a sale.

Define your action levels in writing, in advance. For example: reduce exposure at 170%, deposit at 150%, do not permit the account below 140%. Written in advance, these are policy. Decided during a sell-off, they are improvisation.

Review after every significant market move, not on a fixed schedule. A monthly review is inadequate when a week can consume half your buffer.

Reduce leverage into strength, not weakness. The time to lower the balance is after a rally, when selling is voluntary and priced well. Almost everyone intends to do this; very few do.

What good looks like

A well-run levered portfolio is unexciting by design:

  • Loan balance around half of available capacity
  • Maintenance ratio comfortably above 180% in normal conditions
  • No single position above 10% of gross exposure
  • Every holding exitable within two days at reasonable cost
  • Cash reserve outside the account equal to ~10% of the balance
  • Written action levels, reviewed after every material move

None of it is complicated. All of it is easy to abandon during a strong market, which is exactly when abandoning it is most expensive.

The asymmetry to remember

Leverage magnifies gains and losses symmetrically in percentage terms, but the consequences are asymmetric. A gain leaves you with a larger portfolio and full discretion. A loss of the same magnitude can leave you with a smaller portfolio and no discretion at all, because the decision has been transferred to someone whose only objective is recovering their loan.

Manage the facility so that decision never transfers.

This article is general information and not investment advice. Leveraged trading carries a high level of risk and losses can exceed your initial deposit.