Ever quoted a price that felt tight, only to realise later you barely covered the direct costs? That is gross margin in action, or rather its absence. Gross margin measures the percentage of revenue left after paying for the direct inputs of your product or service, and it is the first place to look when profitability disappoints.
For a UK limited company or sole trader, the calculation is simple: (revenue minus cost of goods sold) divided by revenue, multiplied by 100. Cost of goods sold (COGS) includes raw materials, direct labour, subcontractor costs, and any consumables exclusively tied to delivering a sale. It excludes rent, marketing, administrative salaries, utilities, and your own drawings or salary. A common trap is misclassifying overheads as COGS, which inflates the margin and masks underlying inefficiency.
Take a manufacturing SME as an example. You sell a batch of bespoke furniture for £80,000. The timber, hardware, and specialist finishes cost £18,000. Your two joiners are paid a combined £28,000 in gross wages plus employer's NI and pension contributions of £4,200. Direct workshop consumables (sanding discs, glue, lacquer) add another £1,800. Total COGS: £52,000. Gross profit: £28,000. Gross margin: 35%. That is below the 40-60% benchmark for most product-based businesses and signals a need to review pricing, material waste, or production efficiency.
For service businesses such as consultancies or software developers, COGS typically comprises the salaries, employer NI, and pension of billable staff, plus any third-party licences or tools used exclusively for client work. A consultancy generating £200,000 in fees with £90,000 in direct staff costs and £10,000 in software subscriptions has a gross margin of 50%. That leaves £100,000 to cover rent, marketing, your own salary, and corporation tax.
Gross margin is not net profit margin. Net profit margin deducts every operating expense, including your office lease, insurance, travel, and professional fees. Corporation tax at 19% (profits under £50,000) or 25% (profits over £250,000) applies to net profit, not gross margin. But a weak gross margin means you enter that tax calculation with less buffer, making it harder to pay dividends (taxed at 8.75% to 39.35% depending on your income band) or reinvest in equipment and staff.
Why this matters for your business
Gross margin is the primary driver of sustainable pricing. If you are losing money on every job, no volume of sales will fix it. Track gross margin per project or product line monthly, not annually. Benchmark against the 40-60% range for UK service and product businesses. If your margin sits persistently below 30%, investigate scope creep, utilisation rates, or whether you are absorbing costs you should charge separately. Above 70% may indicate you are underinvesting in quality or missing opportunities to scale delivery capacity.