Margin financing — sometimes called margin lending or securities-backed lending — is a facility that lets an investor borrow money using the securities already held in their account as collateral. Instead of selling positions to free up cash, or waiting for new funds to settle, the investor draws on a credit line secured against the portfolio.

For active traders and professional investors this is one of the most direct ways to increase market exposure. It is also one of the most misunderstood, because the arithmetic that makes it attractive in a rising market is exactly the arithmetic that makes it punishing in a falling one.

The basic mechanism

When you open a margin facility, three numbers govern everything that follows:

  1. Portfolio value — the market value of the eligible securities you hold.
  2. Loan-to-value (LTV) — the proportion of that value the lender is prepared to advance against each asset.
  3. Loan balance — how much you have actually drawn.

Suppose you hold £400,000 of large-cap equities with a 70% LTV. Your maximum borrowing capacity is £280,000. If you draw £200,000, your total market exposure becomes £600,000 against £400,000 of your own capital — a gross exposure of 1.5x.

The loan does not have a fixed repayment schedule in the way a mortgage does. It sits against the account, accrues interest daily, and can typically be repaid at any time without penalty.

How the interest works

Two mechanical details matter more than the headline rate:

  • Daily accrual. Interest is calculated on the outstanding balance each day, not on the peak balance or the facility limit. If you borrow for four days, you pay for four days.
  • Monthly settlement. The accrued interest is aggregated and charged once a month, which keeps the accounting simple and avoids a drag on daily cash management.

Most institutional lenders price the facility as a benchmark plus a spread. The benchmark is a published overnight reference rate — SONIA for sterling, SOFR for US dollars, EURIBOR for euros — and the spread is the lender’s margin, usually tiered so that larger balances attract a tighter spread.

The arithmetic is straightforward:

Daily interest = Loan balance × (Benchmark + Spread) ÷ 360

On a £200,000 balance at a 6.00% all-in annual rate, the daily cost is roughly £33.33 and the monthly cost around £1,000. Whether that is expensive depends entirely on what the borrowed capital is doing.

Where margin financing makes sense

There are four situations where a margin facility is genuinely useful rather than merely available:

Bridging settlement. You have sold one position and identified another, but the proceeds have not settled. Drawing briefly on margin avoids missing the entry.

Avoiding a forced sale. You need liquidity for a reason unrelated to the portfolio. Borrowing against holdings can be cheaper than realising a position and crystallising a tax event.

Measured leverage on high-conviction positions. An investor with a genuine edge can amplify it. The word doing the work in that sentence is measured.

Portfolio efficiency. Holding a diversified book and financing a portion of it can be more capital-efficient than concentrating into fewer names to achieve the same exposure.

Where it goes wrong

Leverage is symmetric in its arithmetic and asymmetric in its consequences. Three failure modes recur:

Ignoring the maintenance level. Borrowing capacity is calculated on today’s market value. If the market falls, capacity falls with it — while the loan balance stays exactly where it was. This is why margin calls tend to arrive at the worst possible moment.

Financing illiquid or concentrated positions. A single-stock portfolio at high LTV is not a leveraged portfolio; it is a countdown. Lenders apply lower LTVs to concentrated and less liquid holdings precisely because the exit is harder.

Treating the facility as permanent capital. A margin loan is callable and its terms are reviewable. It is a tool for defined purposes over defined periods, not a substitute for equity.

The questions to ask any lender

Before signing, get clear answers on:

  • Is pricing benchmark-linked and published, or discretionary?
  • Are there arrangement, commitment or non-utilisation fees?
  • What LTV applies to each asset class you actually hold?
  • At what level is a margin call triggered, and how long do you have to respond?
  • At what level does forced liquidation begin, and how is it executed?
  • How are rates reviewed, and what notice is given of a change?

A lender that answers all six clearly and in writing is a lender you can plan around. One that does not is a risk you have not priced.

In summary

Margin financing is a precise instrument. It increases exposure without requiring you to dismantle a portfolio you have built deliberately, and when priced transparently against a published benchmark, its cost is knowable in advance. The discipline it demands is not complicated — know your maintenance level, keep genuine headroom, and never let the facility become a position you did not choose.

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