What is COGS (Cost of Goods Sold)?
COGS (Cost of Goods Sold) represents the direct costs you incur to produce or acquire the products you sell. For most e-commerce businesses buying from suppliers, this means the unit purchase price plus any costs directly attributable to getting that product to your warehouse.
Why COGS Matters for Advertising
Your COGS determines your gross margin — the amount left after product costs. That gross margin is the pool from which you fund shipping, payment fees, advertising, and profit. Without accurate COGS, every advertising decision is a guess.
What to Include in COGS
- Unit purchase price — What you pay your supplier per unit (ex-VAT)
- Import duties and tariffs — Customs charges on imported goods, allocated per unit
- Inbound freight — Cost to ship products from supplier to your warehouse, allocated per unit
- Manufacturing costs — Direct materials and labour if you produce your own products
- Product packaging — Boxes, bags, and inserts that are part of the product itself
What Is NOT Traditional COGS
In accounting, these costs sit below the gross profit line. They are real costs, but they are not included in the narrow accounting definition of COGS:
- Outbound shipping — The cost to ship orders to customers (operating expense)
- Payment processing fees — Stripe, PayPal, and card fees (operating expense)
- Platform fees — Shopify subscription, Amazon referral fees (operating expense)
- Advertising spend — This becomes part of your CAC calculation
- Warehouse rent and staff wages — Overhead, not direct product cost
Accounting COGS vs. Advertising Decisions
Accounting COGS is fine for your P&L. But for advertising decisions, you cannot stop there. Payment fees, outbound shipping, and returns all reduce the money available for ads. Ignoring them leads to bids that look profitable on paper but lose money in practice. GROW's MarginStack uses a complete cost picture — what we call COGS+ — for every bidding decision.
What is CAC (Customer Acquisition Cost)?
CAC (Customer Acquisition Cost) is the total cost to acquire a new customer. For e-commerce brands running paid advertising, advertising spend dominates this figure — but a complete CAC calculation includes all marketing and sales costs.
What to Include in CAC
- Paid advertising — Google Ads, Meta Ads, TikTok Ads, Bing Ads
- Affiliate commissions — Payments to affiliates for referred sales
- Influencer fees — Paid partnerships for product promotion
- Marketing tools — Email platforms, SMS tools, analytics subscriptions
- Agency fees — If you use a marketing or PPC agency
- Marketing salaries — The portion of team time spent on acquisition
For e-commerce with repeat customers, Cost Per Order is often more actionable than CAC because it reflects what you spent to generate each transaction — including returning customers — rather than only first-time buyers.
Formulas and Worked Example
Core Formulas
COGS Formula (per product)
For per-product bidding decisions — which is what matters for advertising — use the unit-level calculation:
Product COGS = Unit Purchase Price + Import Duty + Inbound Freight (per unit)
Gross Margin Formula
Gross Margin % = ((Net Revenue − COGS) ÷ Net Revenue) × 100
Always calculate gross margin on net (ex-VAT) revenue. Calculating on gross revenue including VAT inflates your apparent margin — the VAT you collect belongs to the government, not you.
CAC Formula
CAC = Total Marketing & Sales Costs ÷ Number of New Customers Acquired
Cost Per Order = Ad Spend ÷ Total Orders
Contribution Margin Formula
Your contribution margin is what remains after all variable costs except advertising. This is the ceiling for ad spend:
Contribution Margin = Net Revenue − COGS − Shipping − Payment Fees − Platform Fees − Return Costs
Maximum Profitable Ad Spend
Max Ad Spend = Contribution Margin − Target Profit (£)
LTV Formula
LTV = Average Order Value × Purchase Frequency (per year) × Customer Lifespan (years)
Worked Example: £100 Selling Price
A retailer sells a home goods product at £100 including VAT (20%).
Step 1 — Net Revenue: £100 ÷ 1.20 = £83.33
Step 2 — COGS: Supplier price £30 + import duty £3 + inbound freight £2 = £35.00
Step 3 — Gross Margin: (£83.33 − £35.00) ÷ £83.33 = 58%
Step 4 — Other Variable Costs:
Outbound shipping: £5.00
Payment fee (2.9%): £2.42
Platform fee (2%): £1.67
Return provision (8% of COGS + shipping): £3.20
Total other costs: £12.29
Step 5 — Contribution Margin: £83.33 − £35.00 − £12.29 = £36.04
Step 6 — Target Profit (10% of net revenue): £8.33
Step 7 — Maximum Ad Spend per Sale: £36.04 − £8.33 = £27.71
Step 8 — Implied Target ROAS: £83.33 ÷ £27.71 = 3.0× (300%)
If your actual Cost Per Order is currently £35, you are spending £7.29 more per sale than your economics support — meaning you are losing money on every order at your current ROAS target.
Per-Product vs. Average Calculations
The example above uses one product. When you have 200 SKUs with costs ranging from £5 to £200, a single average COGS leads to catastrophically wrong bids. Products with thin margins get overspent; high-margin products get underspent. Per-SKU margin tracking is the only accurate approach at scale.
Understanding Your True Cost Stack
For every sale, there are multiple layers of costs that reduce your margin. Accounting separates these into COGS and operating expenses — but for advertising decisions, every variable cost per sale matters equally. Here is how the layers stack on a typical £100 product:
| Cost Layer | Typical % of Selling Price | Example (£100 sale) | Notes |
|---|---|---|---|
| Product COGS | 25–50% | £35.00 | Supplier price + duty + inbound freight |
| VAT (UK 20%) | ~17% of gross | £16.67 | Not yours to keep — reduces net revenue |
| Outbound Shipping | 3–8% | £5.00 | Higher for bulky or international orders |
| Payment Processing | 1.5–3% | £2.42 | Stripe, PayPal, card fees |
| Platform Fee | 0–15% | £1.67 | Shopify = ~2%; Amazon = 8–15% |
| Returns Provision | 1–8% | £3.20 | Fashion returns can exceed 25% rate |
| Total Before Ads | ~63% | £63.96 | Leaves £36.04 for ads and profit |
| Advertising (CAC) | 15–35% | £20.00 | Your target must fit within the margin |
| Net Profit | 5–20% | £16.04 | After all costs at this example level |
The Hidden Cost Problem
A brand running 3× ROAS (33% of revenue on ads) with 40% COGS and 10% other variable costs is already at 83% of net revenue spent before profit. After VAT (reducing net revenue), returns, and operating overhead, they are often losing money on every sale — while reporting positive ROAS in their ad platform.
Industry Benchmarks
These benchmarks give you reference points for where your costs and margins should sit. Remember that healthy businesses can operate outside these ranges — but if you are significantly different, you need a clear reason why.
Gross Margin by Industry
| Industry | Typical Gross Margin | Notes |
|---|---|---|
| Fashion & Apparel | 50–70% | Higher for DTC brands; lower for resellers of branded goods |
| Beauty & Cosmetics | 60–80% | High-margin category; strong brand premium possible |
| Health & Supplements | 55–75% | Subscription models often achieve the upper end |
| Home & Garden | 40–55% | Varies significantly by product type and AOV |
| Food & Beverage | 35–50% | Perishables typically at the lower end; premium DTC brands higher |
| Electronics | 20–40% | Highly competitive; thin margins require volume or high AOV |
| Sports & Outdoor | 40–55% | Technical products often command better margins than commodities |
| Toys & Hobbies | 35–50% | Seasonal demand patterns create margin pressure in off-peak |
CAC Benchmarks by Industry
| Industry | Average CAC | Healthy Range | Channel Notes |
|---|---|---|---|
| Fashion DTC | £25–45 | £15–35 | High competition in paid social; Google Shopping often more efficient |
| Beauty | £20–40 | £15–30 | Strong organic potential can reduce blended CAC significantly |
| Electronics | £30–60 | £20–50 | Higher AOV supports higher CAC; strong comparison shopping behaviour |
| Home & Living | £35–55 | £25–45 | Google Shopping often most efficient; visual intent matches well |
| Subscriptions | £40–80 | £30–60 | Higher CAC acceptable when LTV is 12+ months of recurring revenue |
How to Use These Benchmarks
Benchmarks are a starting point, not a target. Your actual profitable CAC ceiling is determined by your specific margins — not the industry average. A brand with 70% gross margins can afford to pay more per customer than one with 30% gross margins, even in the same category.
Common COGS & CAC Mistakes
These mistakes cost e-commerce brands real money — not in dramatic single events, but through quiet, sustained margin erosion that is hard to see until you do the maths properly.
Calculating Margin on Gross Revenue
If you are VAT-registered, the 20% VAT you collect is not your revenue — it belongs to HMRC. Calculating margins on £100 (gross) instead of £83.33 (net) makes every product look 20% more profitable than it is. Always use ex-VAT revenue as your baseline.
Using a Single Average COGS
A single average COGS across your catalogue causes systematic over-bidding on low-margin products and under-bidding on high-margin ones. If you sell products ranging from £10 to £200 purchase price, the average is meaningful for the P&L but useless for per-product advertising decisions.
Ignoring Returns in Margin Calculations
Returns are not just a lost sale — you have already paid for advertising, shipping, and payment processing. A 20% return rate on a £100 product with £5 shipping and £2.50 payment fees adds roughly £15 of sunk cost for every five sales. That is 3% off your effective margin, invisible until you account for it.
Omitting Payment Fees from Ad Budgets
Stripe charges 1.5–2.9% + a fixed fee per transaction. On a £50 order at 2.9%, that is £1.65 — money you cannot spend on advertising. At scale, payment fees can represent 2–4% of revenue, which translates directly to a higher required ROAS target.
Using the Same ROAS Target for All Products
A 4× ROAS target makes sense for a product with 60% gross margin. Applied to a product with 25% gross margin, it guarantees a loss after shipping, fees, and returns. ROAS targets should be calculated individually from each product's contribution margin.
Including Fixed Overhead in Product COGS
Warehouse rent, staff wages, and software subscriptions are real costs — but they are fixed overheads, not per-unit product costs. Including them in COGS inflates per-product cost and creates incorrect per-unit margins. Keep them in your operating expense analysis separately.
LTV:CAC — The Ultimate Health Check
CAC tells you what you spent to acquire a customer. LTV tells you what that customer is worth over the entire relationship. The ratio between them is the most important strategic metric in e-commerce.
LTV Formula
LTV = Average Order Value × Purchase Frequency (per year) × Customer Lifespan (years)
Example: LTV Calculation
Average Order Value: £75
Average purchases per year: 2.5
Average customer lifespan: 3 years
LTV = £75 × 2.5 × 3 = £562.50
At this LTV, you can afford a CAC of up to £187.50 to maintain a 3:1 ratio. If your current CAC is £45, you have significant headroom to invest more aggressively in acquisition than competitors who only optimise for first-order profitability.
LTV:CAC Ratio Benchmarks
| Ratio | Status | What It Means | Action |
|---|---|---|---|
| < 1:1 | Critical | Losing money on every customer acquired | Reduce CAC urgently or exit the channel |
| 1:1 – 2:1 | Warning | Marginal economics, not sustainable at scale | Optimise acquisition and improve retention |
| 3:1 | Target | Industry standard — sustainable growth possible | Maintain and look for selective scale opportunities |
| 4:1 – 5:1 | Excellent | Strong unit economics, healthy business | Consider increasing spend to capture more market share |
| > 5:1 | Underinvesting | You are leaving growth on the table | Scale acquisition aggressively while economics hold |
Why LTV Changes the Advertising Game
Brands that know their LTV can rationally outbid first-purchase-focused competitors. If your customer LTV is £500 and your CAC is £80, you are at a 6:1 ratio — meaning you could profitably increase CAC to £150 and still be at 3:1, reaching customers your competitors cannot afford to target.
MarginStack: From Cost Data to Profitable Bids
Calculating COGS and contribution margins accurately for one product takes a few minutes. Doing it for 500 products, keeping it updated when supplier prices change, and feeding that data into advertising bids automatically — that is where manual processes break down.
What is MarginStack (COGS+)?
MarginStack is GROW's complete cost management system — what we call COGS+. It captures every cost layer for every product: traditional COGS, outbound shipping, payment fees, platform fees, import duties, and return rate provisions. That complete cost picture feeds directly into profit-based bid calculations at the SKU level.
How MarginStack Works
- CSV Upload — Bulk import product costs directly from supplier price lists
- Google Sheets Sync — Connect your live cost spreadsheet so margins update automatically when suppliers change prices
- Global Cost Layers — Configure account-wide settings for shipping rates, payment processor fees, and platform fees
- Per-Product Overrides — Set specific costs for products that differ from your defaults (different suppliers, unusual shipping, etc.)
- Automatic Margin Recalculation — When selling prices change in your product feed, margins recalculate automatically
- ProfitClarity Integration — Margin data feeds directly into per-SKU ROAS target calculations for your Google Shopping campaigns
From Cost Data to Bid Strategy
Once MarginStack is configured, GROW's ProfitClarity system calculates the maximum profitable bid for every product in your catalogue:
Max CPC = (Net Sale Price − All Variable Costs − Target Profit) × Conversion Rate
Every product gets a ROAS target derived from its actual economics — not a single platform-wide number applied regardless of margin. High-margin products get more aggressive targets; thin-margin products get conservative targets that prevent loss-making spend.
Validating Margins with Sale Analysis
MarginStack calculates expected margins. Sale Analysis validates them against actual sales data. If a product shows a 5% return rate in MarginStack but your actual return data shows 18%, Sale Analysis surfaces that discrepancy so you can correct your cost model before advertising spend compounds the error.
Frequently Asked Questions
What is the difference between COGS and total cost per sale?
COGS covers only direct product costs: supplier price, import duty, and inbound freight. Total cost per sale also includes outbound shipping, payment processing fees, platform fees, and a return provision — all of which reduce the margin available for advertising and profit. For advertising decisions, you need the full picture, not just accounting COGS.
How do I calculate Customer Acquisition Cost (CAC)?
Divide your total marketing and sales spend in a period by the number of new customers acquired. For e-commerce, Cost Per Order (total ad spend ÷ total orders) is often more actionable on a daily basis, since it reflects what you actually paid in advertising per transaction — including repeat customer orders.
What gross margin should my e-commerce business target?
It depends on your category. Fashion and beauty typically sustain 50–70%+ gross margins. Electronics and general retail typically run 20–40%. The key test is that your gross margin must be high enough to absorb shipping, payment fees, advertising (CAC), returns, and still leave a meaningful net profit after all operating costs.
What is a healthy LTV:CAC ratio for e-commerce?
The industry standard target is 3:1 — a customer generates three times their acquisition cost in lifetime value. Ratios below 2:1 suggest a marginal or unprofitable business model. Above 5:1 often means you are underinvesting in growth and leaving revenue on the table — competitors with similar or worse economics may be scaling faster simply by reinvesting more aggressively.
Why calculate margins per product rather than using a catalogue average?
Using average COGS for advertising decisions means you systematically overbid on low-margin products and underbid on high-margin ones. A product with 20% gross margin and one with 60% gross margin require completely different ROAS targets to be profitable. Per-product margins are the only way to bid accurately across a diverse catalogue without inadvertently subsidising unprofitable sales.
Next Steps
Understanding COGS and CAC is the foundation. Applying it consistently across hundreds of products, keeping it updated as costs change, and automatically translating it into profitable bids — that is where GROW helps e-commerce brands at scale.
Put Your Cost Data to Work with GROW
GROW's MarginStack (COGS+) captures every cost layer per SKU and feeds it directly into profit-first bidding with ProfitClarity. Import your costs via CSV or Google Sheets sync, configure your cost layers once, and let GROW calculate and apply the right ROAS target for every product automatically.
