Cost of Goods Sold (COGS): What It Is and How to Calculate It
The cost of what sold. Not everything you bought.
From stock to the income statement.
A hypothetical month at a homeware shop.On this page
Cost of Goods Sold, usually shortened to COGS, is the cost assigned to the products a business sold during a period. It connects sales on the income statement with the inventory that left the business. If a shop buys ten items but sells six, COGS reflects the cost of the six sold items, not all ten purchased items.
COGS helps show how much gross profit remains after paying for the goods delivered to customers. It does not include every cost of running the business.
The idea to remember
Bought is not the same as sold. Unsold stock remains inventory.
What is Cost of Goods Sold?
COGS is the cost of inventory recognized as an expense when the related goods are sold. For a retailer, it normally begins with the purchase cost of merchandise and directly attributable costs needed to bring it to its present location and condition. For a manufacturer, inventory cost can also include direct materials, direct production labor and allocated production overhead.
The exact treatment depends on the applicable accounting rules and the nature of the business. Service companies may use a related measure called cost of services or cost of revenue instead.
Why does it matter?
COGS helps a business:
- calculate gross profit;
- understand whether product costs are rising or falling;
- support pricing and purchasing decisions;
- connect inventory records with the income statement.
Revenue can increase while gross profit weakens if the cost of the products sold rises faster than sales. COGS makes that change visible.
The basic formula
For a retailer using a periodic inventory system:
COGS = Beginning inventory + Net purchases - Ending inventory
- Beginning inventory is the cost of goods available at the start of the period.
- Net purchases are inventory purchases adjusted for items such as purchase returns and discounts. Directly attributable freight or duties may also form part of inventory cost.
- Ending inventory is the cost of goods still held at the end of the period.
Beginning inventory plus net purchases equals goods available for sale. Subtracting ending inventory separates the cost of goods sold from the cost that remains as an asset.
Businesses using a perpetual inventory system update inventory and COGS as sales occur. A physical inventory count is still important because damage, theft, recording errors and other differences can make the records inaccurate.
A simple example
Hypothetical example: A small homeware shop starts the month with EUR 2,000 of inventory. During the month, it makes EUR 8,000 of net inventory purchases. At month-end, the inventory still on hand costs EUR 2,500.
COGS = EUR 2,000 + EUR 8,000 - EUR 2,500 = EUR 7,500
If the shop generated EUR 12,000 in sales, its gross profit before other operating expenses would be:
Gross profit = EUR 12,000 - EUR 7,500 = EUR 4,500
The EUR 2,500 of ending inventory is not an expense in this example because those goods have not yet been sold. Inventory losses or write-downs can require separate expense recognition under the applicable rules.
When should you use it?
Use COGS when:
- preparing or reviewing an income statement;
- calculating gross profit or gross margin;
- examining product pricing and purchasing costs;
- analyzing inventory performance;
- building unit economics for a product or order.
Track it consistently over comparable periods. A monthly comparison can reveal cost changes sooner than an annual total.
How to interpret the result
COGS is not automatically good when low or bad when high. Its meaning depends on the revenue earned and the business model.
A useful companion measure is:
COGS percentage = COGS / Revenue x 100
In the example, COGS is 62.5% of sales. This means EUR 0.625 of each euro of sales was absorbed by the cost of the goods sold, leaving EUR 0.375 before operating expenses.
Compare this percentage with the same business over time, its budget and genuinely similar products. Do not assume that one universal percentage is healthy for every industry.
Common confusion: COGS vs operating expenses
COGS relates to the goods sold. Operating expenses support the wider business and are not tied to producing or acquiring those goods in the same way.
Advertising, general administrative salaries, office costs and many selling expenses are usually operating expenses rather than COGS. By contrast, product purchase costs, direct production labor and appropriate production overhead commonly form part of inventory cost.
Classification can require judgment. A cost may vary with sales without automatically belonging in COGS, so businesses should apply a consistent accounting policy.
Common mistakes
- Expensing all purchases immediately even when some goods remain unsold.
- Including general marketing or administrative costs in COGS.
- Excluding directly attributable costs needed to acquire or produce inventory.
- Using an inaccurate ending inventory count.
- Changing inventory cost methods or classifications without explaining the change.
- Comparing COGS percentages across businesses that classify costs differently.
Limitations
COGS does not show total profitability, cash flow or the full cost of serving a customer. Inventory valuation methods and estimates can also change the reported amount. Use COGS with gross profit, operating expenses and unit economics, and obtain accounting advice when classification or reporting rules are uncertain.
Quick checklist
Put it to work
Calculate one month of COGS in 20 minutes
Use one completed month and gather four figures: beginning inventory, inventory purchases, purchase returns or discounts, and ending inventory. Add revenue for the same period to calculate gross profit and the COGS percentage.
- Calculate net purchases by subtracting purchase returns and discounts from purchases.
- Add beginning inventory and net purchases.
- Subtract ending inventory to calculate COGS.
- Subtract COGS from revenue to calculate gross profit.
- Divide COGS by revenue and multiply by 100.
- Compare the result with the previous month and write one possible reason for any meaningful change.
Before acting, verify that both months use the same inventory method and cost classifications.
Inventory at cost. Purchases include eligible acquisition costs; revenue is after sales returns and discounts. Currency changes labels, not amounts.
This month: the calculation
- Net purchases
- €8,000
- Goods available
- €10,000
- Less ending inventory
- €2,500
- COGS
- Gross profit
- €4,500
- COGS / revenue
- 62.5%
- Gross margin
- 37.5%
Gross profit remains before operating expenses, interest and tax.
Inventory at cost. Purchases include eligible acquisition costs; revenue is after sales returns and discounts. Currency changes labels, not amounts.
Previous month: the calculation
Optional comparison. Add all five previous-month amounts, including zeros where applicable.
Month-to-month change
No comparison yet. Previous-month figures are optional.
Key takeaways
- COGS is the cost of products sold during a period, not the cost of every product purchased.
- A basic periodic formula is beginning inventory plus net purchases minus ending inventory.
- Revenue minus COGS equals gross profit.
- COGS and operating expenses describe different layers of business cost.
- Consistent inventory counts and cost classifications are essential for useful comparisons.
Final takeaway
COGS is the cost of the products actually sold during a period. The basic inventory formula prevents a business from treating unsold stock as if it had already been consumed.
Calculate it consistently, compare it with revenue and remember what it does not include. COGS explains gross profit, not the final profit of the business.