The Second Line of Your Accounts, and the Most Likely to Be Wrong
Almost every set of UK company accounts opens the same way. Turnover, then cost of sales, then gross profit. Two numbers and a subtraction, done before you reach line four.
The first number is easy. Turnover is what you invoiced, and if it is wrong you usually know about it. The second number is not easy at all. Cost of sales depends on a stock count, on a set of judgement calls about which costs are direct, and on a valuation method that most business owners have never been asked to choose. Get it slightly wrong and every figure below it moves, including the profit you pay tax on.
This guide explains what cost of sales is, gives you the formula, walks through a worked example, and covers the specific places it goes wrong in owner-managed businesses. It also makes a point you will rarely see stated plainly: the Companies Act requires this line but never defines it, which has consequences for anyone trying to benchmark their margin against anybody else.
What Cost of Sales Actually Is
Cost of sales is the direct cost of the things you sold during the period. Not the things you bought, and not the things you still have sitting in the stockroom. The things you actually sold.
That distinction is the whole idea. If you buy £100,000 of stock in a year and sell three quarters of it, your cost of sales is £75,000, not £100,000. The remaining £25,000 has not become a cost yet. It is an asset on your balance sheet waiting for a customer. This is the matching principle doing its job: the cost of an item lands in the same period as the income from selling it, so gross profit means something.
The test for whether a cost belongs here is direct causation. Would you have incurred the cost if the sale had not happened? Raw materials, yes. The wholesale price of a product, yes. Factory rent, no, that runs whether or not you sell anything, so it belongs with your overheads further down the page.
Cost of Sales and Cost of Goods Sold: Same Thing, Different Passport
Cost of goods sold, usually shortened to COGS, means the same as cost of sales. The difference is geographic rather than technical. Cost of sales is the statutory UK term, appearing word for word in the profit and loss formats set out in company law. Cost of goods sold is the American term, and it dominates online search results because most accounting content is written for a US audience.
This matters more than a naming quibble, and we come back to it below, because some of what US sources teach about valuing stock is not permitted in UK accounts at all.
You may also see cost of revenue, which software and service businesses often prefer because "goods" sits awkwardly when you sell a subscription. It means the same thing again.
The Cost of Sales Formula
For any business that holds stock, the formula is:
Cost of sales = opening stock + purchases − closing stock
Opening stock is what you were holding at the start of the period, which is last year's closing figure. Purchases are what you bought during the period. Closing stock is what you counted at the end.
Manufacturers and anyone converting materials into a finished product add the direct costs of doing the converting:
Cost of sales = opening stock + purchases + direct labour + production overheads − closing stock
For a service business with no stock at all, the calculation collapses to the cost of delivering the work, which in practice means the salaries and subcontractor costs of the people doing the billable jobs.
A Worked Example
A homeware retailer for the year to 31 March 2026.
| Item | Amount |
|---|---|
| Turnover | £480,000 |
| Opening stock at 1 April 2025 | £62,000 |
| Purchases | £310,000 |
| Carriage in (delivery from suppliers) | £6,000 |
| Closing stock at 31 March 2026 | £58,000 |
Cost of sales = £62,000 + £310,000 + £6,000 − £58,000 = £320,000
Gross profit = £480,000 − £320,000 = £160,000
Gross margin = (£160,000 / £480,000) × 100 = 33.3 percent
Two details in that table are worth pausing on. Carriage in belongs in cost of sales because it is part of what it cost to get the goods ready to sell. Carriage out, the cost of delivering to your customer, does not: it is a distribution cost and sits below gross profit. Businesses mix these up constantly, and because the two often arrive on the same courier invoice, nobody notices.
What Goes In and What Stays Out
| In cost of sales | In overheads |
|---|---|
| Wholesale cost of goods sold | Rent and rates on offices |
| Raw materials and components | Admin, finance and management salaries |
| Direct and production labour | Marketing and advertising |
| Subcontractors on billable work | Accountancy, legal and insurance |
| Carriage in and import duty | Carriage out and delivery to customers |
| Production overheads absorbed into stock | Software not tied to delivery |
| Stock written off or shrinkage | Bank charges and interest |
Some costs genuinely sit on the line, and packaging is the classic example. Packaging that forms part of the product goes in cost of sales. Packaging used to post it goes in distribution. Whichever you choose, choose once and keep it, because a cost that moves between the two categories changes your gross margin without anything real having changed in the business.
The Closing Stock Trap: How to Invent Profit by Accident
Here is the thing about cost of sales that catches people out. It looks like a profit and loss figure, but it is really a balance sheet figure in disguise. Look at the formula again. Purchases you can verify against invoices. Opening stock is fixed by last year's accounts. The only number with any give in it is closing stock, and closing stock is whatever somebody counted on a clipboard.
Follow that through. Suppose our retailer's stocktake is generous and closing stock is recorded at £68,000 rather than £58,000.
| Correct | Overstated by £10,000 | |
|---|---|---|
| Cost of sales | £320,000 | £310,000 |
| Gross profit | £160,000 | £170,000 |
| Gross margin | 33.3 percent | 35.4 percent |
Ten thousand pounds of profit has appeared out of a counting error. At the 19 percent small profits rate that is £1,900 of corporation tax on money the business never made. Worse, the error does not stay put. That inflated closing stock becomes next year's opening stock, so year two absorbs a £10,000 cost that belonged to year one. You have paid tax early and produced two consecutive years of misleading figures from one bad afternoon in the stockroom.
The reverse works the same way. Understate closing stock and you understate profit, which sounds like a tax win until the reversal lands next year, or until you take the accounts to a lender or a buyer and they see a margin that does not reflect the business.
Our practical rule: watch the gross margin percentage, not the stock figure. Nobody can eyeball whether £58,000 of stock is right. Everybody can spot that the margin jumped from 33 percent to 35 percent in a year when prices did not move. If the margin shifts by more than a point or two and you cannot name the reason, the stocktake is the first place to look. That single check catches more errors than any amount of staring at the stock sheets.
Valuing the Stock: What UK Rules Actually Require
Counting the units is the easy half. Putting a value on them is where the rules come in, and UK accounts prepared under FRS 102 have to follow Section 13.
Stock is carried at the lower of cost and estimated selling price less costs to complete and sell. If you paid £30 for something you can now only shift for £18, it goes in at £18. Slow-moving and obsolete stock has to be written down, and that write-down runs through cost of sales in the year you spot it, not the year you eventually skip it.
Cost includes production overheads, not just materials. This is the rule most owner-managed manufacturers miss. Fixed production overheads are allocated to stock based on normal capacity, meaning the output you would expect on average, so a quiet month does not let you load more overhead onto each unit. A workshop valuing finished goods at material cost alone is understating its closing stock, which overstates cost of sales, which understates profit until the accountant corrects it at the year end and the figures lurch.
LIFO is not allowed. Where individual items are not distinguishable you use first in, first out or weighted average cost. Last in, first out is prohibited under UK GAAP and under international standards, and HMRC does not accept it for tax either. It is, however, permitted in the United States, which is why so much online COGS guidance walks you carefully through a method you cannot legally use in a set of UK accounts. If you have been following an American template, this is the first thing to check.
The Service Business Problem: A 100 Percent Gross Margin Tells You Nothing
Plenty of agencies, consultancies and trades run a profit and loss account with no cost of sales at all. Every wage sits in administrative expenses, gross profit equals turnover, and the gross margin is a proud and useless 100 percent.
Take an agency billing £600,000, with six delivery staff costing £240,000 and three admin and sales staff costing £120,000. Put all £360,000 in administrative expenses and the accounts show £600,000 of revenue, no cost of sales and £240,000 of operating profit. Perfectly legal, and it tells the owner nothing about whether the work is priced properly.
Split it as it should be split, with the six delivery salaries in cost of sales, and the picture changes:
| Everything in overheads | Delivery staff in cost of sales | |
|---|---|---|
| Turnover | £600,000 | £600,000 |
| Cost of sales | £0 | £240,000 |
| Gross profit | £600,000 | £360,000 |
| Gross margin | 100 percent | 60 percent |
| Overheads | £360,000 | £120,000 |
| Operating profit | £240,000 | £240,000 |
The bottom line is identical. The usefulness is not. The second version tells you that delivery consumes 40p of every pound billed, which is the number you need before you quote the next job, hire the next person, or work out whether the client who negotiated you down is actually making you money. The first version cannot answer any of those questions.
This one is worth sorting out even though the filed accounts are fine either way, and that is precisely why it goes unfixed for years: nothing forces the issue. The accounts that satisfy Companies House are not the same accounts that run a business.
Our View: Nobody Defines the Line Everybody Benchmarks
Cost of sales is required by law. Format 1 of the statutory profit and loss account lists it as item 2, right after turnover. What the law does not do, anywhere, is say what belongs in it. The only note attached is a reminder that the figure is stated after any necessary provisions for depreciation or diminution in value. Beyond that, the composition of the most scrutinised line in UK accounts is an accounting policy, not a legal definition.
That has a consequence people rarely think through. Two genuinely identical businesses can report gross margins ten or fifteen points apart, both correctly, purely because one classifies delivery labour and warehouse costs as direct and the other does not.
It gets more awkward when you try to look the figures up. Format 2 of the statutory accounts, which analyses costs by nature rather than by function, has no cost of sales line and no gross profit line at all. Neither does the micro-entity format, whose eight lines run turnover, other income, cost of raw materials and consumables, staff costs, depreciation, other charges, tax, and profit or loss. And most small companies currently take the exemption that lets them leave the profit and loss account out of what they file.
Put those together and you get the awkward truth: for a large share of UK companies, the gross margin is simply not obtainable from Companies House, and where it is obtainable it was built on somebody else's classification policy. The filing changes coming in 2028 will force small and micro companies to file a profit and loss account, but they will not standardise what goes in cost of sales, and the micro format still has nowhere to put it.
So our view is this. Industry gross margin benchmarks deserve far less trust than they are usually given, and your own margin history deserves far more. A competitor's published 42 percent is an accounting choice you cannot see. Your own margin, calculated the same way every month, is a genuine signal, and the month it moves is a month worth investigating. Consistency beats comparability here, and it is not close.
Cost of Sales, the Cash Basis and Your Tax Bill
Sole traders and partnerships have had a further wrinkle since 6 April 2024, when the cash basis became the default for calculating taxable trading profits. The old turnover limits went, and the accruals basis is now something you elect into rather than something you grow into.
Under the cash basis there is no opening or closing stock adjustment. You deduct stock when you pay for it. That is genuinely simpler, and for a steady business it makes little difference across a few years. For a business whose stock level is moving, it distorts things badly:
- Growing and building stock? You deduct purchases you have not sold yet, so taxable profit is understated while you grow.
- Shrinking or running stock down? You sell goods you deducted in an earlier year, so taxable profit is overstated exactly when cash is tight.
- Bought on credit and not paid by the year end? No deduction at all this year, however full the stockroom is.
None of that is a loophole and none of it is a penalty. It is timing, and it evens out eventually. But it means the profit on a cash basis self assessment return is not a reliable measure of how the business traded, and a lender looking at it will not be seeing a real gross margin. If stock is a significant part of what you do, either elect for the accruals basis or keep a proper stock figure alongside the tax return so you know your real numbers.
One more tax-adjacent point that costs businesses money quietly. Cost of sales should be recorded net of recoverable VAT. Businesses on the VAT flat rate scheme cannot recover input VAT, so their purchase costs are genuinely gross, their cost of sales is genuinely higher, and their gross margin is genuinely lower than a standard-scheme competitor with identical prices and suppliers. That is a real difference, not a presentational one, and it is another reason to be careful before concluding your margin is behind the market.
Common Cost of Sales Mistakes
- Treating purchases as cost of sales. Without the stock adjustment, cost of sales is just what you bought, and gross profit becomes noise driven by ordering patterns.
- Never counting stock in-year. An annual stocktake means eleven sets of management accounts built on an estimate. Even a rough quarterly count is a large improvement.
- Putting carriage out in cost of sales. Delivery to customers is a distribution cost and belongs below gross profit.
- Leaving stock write-offs out. Damaged, expired and unsellable stock has to come out of the balance sheet and into cost of sales.
- Capitalising overheads that are not production overheads. Sales commission and admin salaries never form part of stock cost.
- Moving costs between categories year to year. Each move breaks your own trend, which is the one benchmark that was worth having.
- Forgetting the owner's own time. In a small business the director doing billable work is a real direct cost, even where remuneration is taken as dividends.
How IAK Can Help
Cost of sales is where bookkeeping meets judgement, and it is the line where small businesses most often end up with figures that are technically filed and practically useless. We set the chart of accounts up so direct costs and overheads are separated properly, put a sensible stock process in place, and produce monthly figures where the gross margin is a number you can act on rather than one you find out about at the year end.
If your margin moves and you cannot explain why, or if your accounts show a gross profit you do not recognise from running the business, get in touch. We work with retailers, manufacturers, trades and service firms across North London, and we would rather fix the coding once than adjust the same errors every March.
Sources
- The Small Companies and Groups (Accounts and Directors' Report) Regulations 2008, Schedule 1, for Profit and Loss Account Format 1 and Format 2 and the note on provisions for depreciation and diminution in value.
- The Small Companies (Micro-Entities' Accounts) Regulations 2013, for the eight-line micro-entity profit and loss account format.
- FRS 102: Inventories under UK GAAP, ICAEW, on measurement at the lower of cost and estimated selling price less costs to complete and sell, the allocation of fixed production overheads on the basis of normal capacity, and the prohibition of LIFO.
- BIM33120: Stock valuation, FIFO not LIFO, HMRC internal manual, on LIFO not being accepted for UK tax purposes.
- BIM33135: Stock valuation, lower of cost and net realisable value, HMRC internal manual, on what constitutes cost for stock valuation.
- Cash basis: Overview, GOV.UK, on the cash basis as the default for unincorporated businesses and the option to elect for the accruals basis.
- Changes to the cash basis for traders, ICAEW, on the removal of the turnover, interest and loss relief restrictions from 6 April 2024.
- Corporation Tax rates and reliefs, GOV.UK, for the 19 percent small profits rate used in the stock error example.