What is the cost of sales and how is it calculated?
Answered 11 March 2026
Based on the sources retrieved, I can provide a focused answer on what "cost of sales" means in a UK tax context. Note that the available sources do not contain a single dedicated statutory definition of "cost of sales" — it is primarily an accounting concept referenced in HMRC guidance.
HMRC Guidance / Practice
What cost of sales is:
Cost of sales represents the direct costs of goods or services that are matched against the sales they relate to in a trading account, in order to arrive at gross profit. Direct costs include items such as goods for resale, transport of those goods, and selling expenses such as sales staff's commissions. These are set against the sales they relate to in a trading account leading to a gross profit. General overheads are then set against gross profit to arrive at net profit (or loss) for the business.
How it is calculated:
Cost of sales is calculated using the standard trading account formula:
Opening Stock + Purchases − Closing Stock = Cost of Sales
HMRC's enquiry guidance confirms this approach in practice. For example, when checking the reliability of stock records, HMRC officers add stock purchases to opening stock figures and then subtract sales of stock — effectively reconstructing the cost of sales figure to verify whether closing stock figures are accurate.
Its role in profit calculations:
HMRC guidance confirms that cost of sales is used to calculate the gross profit rate (GPR) and mark-up rate (MUR), which are key tools in examining business records:
- Gross Profit Rate = Gross Profit as a percentage of total sales
- Mark-Up Rate = Gross Profit as a percentage of cost of goods sold
In practice, HMRC uses these ratios to test whether a business's declared figures are credible, particularly for retail and distributive trades.
Adjustments to cost of sales:
Where a trader takes goods for personal use, the cost of sales figure may need to be adjusted. For example, where goods are purchased through the business but are not items of business stock, "the cost of sales figure should have been adjusted accordingly."
In a transfer pricing context, stock/cost of sales is also one of the more common adjustments that may be encountered when comparing results between a tested party and independent comparables.
Note: "Cost of sales" is an accounting concept rather than a defined statutory term in UK tax legislation. Its tax relevance arises in the computation of trading profits, where the figures must reflect an accurate and complete record of purchases, opening and closing stock. If you need guidance on a specific context (e.g., manufacturing, services, or a particular tax regime), further targeted research would be advisable.
Citation sources
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