Home / Services / Cost of Sales Equation
Business GuideThe cost of sales equation every business owner should understand. Formula, worked examples, and practical ways to improve your margins.
Cost of Sales = Opening Inventory + Purchases − Closing Inventory. This equation tells you the direct cost of producing the goods you sold during a period.
Cost of sales (also called Cost of Goods Sold or COGS) includes all direct costs: raw materials, direct labour, and manufacturing overheads. It excludes indirect costs like marketing, admin and rent.
Why it matters: Gross Profit = Revenue − Cost of Sales. Your gross margin reveals pricing power and production efficiency. Declining margins signal problems before they hit your bottom line.
This guide covers the equation, worked examples for product and service businesses, and strategies to manage cost of sales effectively.
Opening stock + purchases/production costs − closing stock = cost of sales.
Direct materials, direct labour, manufacturing overheads, freight-in.
Marketing, admin salaries, rent, utilities — these are operating expenses.
Direct labour costs and subcontractor fees form your cost of sales.
Gross Profit ÷ Revenue × 100. Track this monthly.
FIFO, LIFO and weighted average — how valuation affects your numbers.
Supplier negotiation, process efficiency, waste reduction, automation.
Compare your gross margin to industry averages to spot issues.
Apply the equation correctly with proper inventory counts.
Monthly gross margin tracking catches problems early.
Compare against industry standards and competitors.
Which products, services or inputs drive your costs?
Negotiate suppliers, improve processes, reduce waste.
Ensure pricing reflects true cost of sales plus target margin.
Cost of sales covers direct production costs. Expenses cover everything else — marketing, admin, rent. Both reduce profit, but they are managed differently.
For service businesses: total direct labour + subcontractor + direct project costs for the period.
Varies hugely: retail 25–50%, manufacturing 20–40%, software 70–90%, services 40–60%. Compare within your industry.
Renegotiate suppliers, improve operational efficiency, reduce waste, automate processes, and review pricing. Small improvements compound significantly.
Cost per acquisition formula explained: how to calculate CPA, what is a good CPA, and
Explore →User acquisition cost explained: formula, benchmarks by industry, and proven strategi
Explore →Affordable SEO in Edinburgh from £495/month: professional search engine optimisation
Explore →Affordable SEO packages for UK small businesses from £495/month. Transparent pricing,
Explore →Free ROI calculator: enter spend, CPC, conversion rate and order value to see revenue
Explore →Google Ads agency for Birmingham businesses: profitable Search, Shopping and Performa
Explore →