Margin (Economics and Finance)

Margin is a word with three main meanings in economics and finance. In business, a margin is the share of revenue a company keeps after certain costs, such as gross margin or net profit margin. In economics, "the margin" refers to the next or last unit of something, and marginal analysis studies how costs and benefits change when one more unit is produced, consumed or hired. In trading, margin is the money or collateral an investor must deposit with a broker or clearing house to borrow money or hold a derivatives position.

The senses are related by the idea of an edge or difference: the gap between price and cost, the edge of a decision, or the buffer between a position's value and the loan behind it. Banking adds others: a lender's margin is the spread it charges over a reference rate, and a bank's overall profitability on lending is its net interest margin. In foreign exchange, the margin a provider adds to the mid-market rate is usually called an FX markup.

A bookshop buys a novel for $6 and sells it for $10. The $4 difference, which is 40% of the selling price, is its margin on that book. Out of that, the shop still has to pay rent and staff.

An economist thinking "at the margin" asks a different question: should the shop stay open one extra hour tonight? The answer depends only on what that extra hour would bring in compared with what it would cost, not on the shop's average day. A trader's margin is different again: it is like a deposit on a rented car, money set aside so the lender is protected if something goes wrong.

A profit margin divides a level of profit by revenue:

A markup divides the same difference by cost instead:

• $\text{Price}$ is the selling price per unit, or total revenue for a whole business.
• $\text{Cost}$ is the relevant cost, such as cost of goods sold for gross margin.

Worked example: the novel bought for $6 and sold for $10 has a margin of $4 \div 10 = 40\%$ and a markup of $4 \div 6 \approx 66.7\%$. Confusing the two is a common pricing error. Companies report gross, operating and net margins; a software firm may have a gross margin above 70%, while a supermarket's net margin is often only a few percent. Persistent high margins can reflect efficiency, strong brands or intellectual property, but may also indicate market power, as in a monopoly. Each margin subtracts a different layer of expenses from revenue: gross margin deducts only the direct cost of goods sold, while net margin deducts all costs, including interest and tax.

Lenders also speak of margins. A floating-rate business loan might be priced at a benchmark such as SOFR or SONIA plus a margin of 2.5 percentage points, with the margin set by the borrower's credit risk, the collateral offered and competition among banks. In card payments, acquirers and processors earn a margin on top of interchange and scheme fees, which merchants see clearly under interchange-plus pricing.

Marginal analysis is a core tool of microeconomics. Firms compare marginal revenue with marginal cost to decide how much to produce; consumers weigh the marginal utility of one more purchase against its price; and governments design taxes around the marginal tax rate, the rate on the next unit of income. In macroeconomics, the marginal propensity to consume measures how much of an extra dollar of income is spent. The "marginal revolution" of the 1870s, led by William Stanley Jevons, Carl Menger and Léon Walras, made this kind of reasoning the foundation of neoclassical economics. A key lesson is that past costs already incurred, known as a sunk cost, should not affect decisions about the next unit.

When investors buy securities partly with borrowed money, the deposit they must put up is margin, and the activity is margin trading. In the United States, the Federal Reserve's Regulation T sets the initial margin for most stock purchases at 50% of the purchase price, and FINRA rules require a maintenance margin of at least 25% of the account's market value, with many brokers setting higher levels. If losses push equity below the maintenance level, the broker issues a margin call, and if it is not met the position may face forced liquidation.

In futures and cleared derivatives, a central counterparty collects initial margin when a position is opened and variation margin daily as prices move. Margin requirements limit leverage and protect the system, but sharp increases during market stress can force sales and drain liquidity, a problem seen in the UK gilt market in September 2022 when pension funds using liability-driven investment strategies faced large collateral calls.

• Investor.gov (US SEC): Margin account