Which Products Are Truly Profitable? How to Calculate the Real Contribution Margin per Item

Revenue Is Not Profit — and Your Dashboard Only Shows One Side

German e-commerce is still growing, but slower than ever: according to bevh, total revenue in 2025 rose just 3.2% to EUR 83.1 billion. The days when pure growth covered all problems are over. For e-commerce leaders, one question is moving to the centre: Which products actually make money?

Not gross revenue. Not gross profit. The real contribution margin per item — after deducting all variable costs.

The problem: this number doesn't exist in most companies. It's scattered across five to ten different systems. And as long as it stays invisible, you're making decisions on incomplete data.

Why Gross Profit Misleads You

When you look at a product today in Shopware, Shopify, or your BI tool, you typically see:

• Revenue
• Cost of goods sold (COGS)
• Gross profit (revenue minus COGS)

A T-shirt priced at EUR 39.90 with EUR 12 in procurement costs shows a gross profit of EUR 27.90 — that looks solid. But between this gross profit and actual earnings lie cost layers that never appear in standard dashboards.

According to K5/Digital Magazin, marketing costs per order have risen 30 to 70% over the past five years. Fulfillment costs have climbed 20 to 40%. And returns — according to the EHI Retail Institute, a single return costs up to EUR 20 per item — are often not allocated at the product level at all.

The result: you optimise for revenue while your most profitable products get lost in the noise and your loss-making items keep getting promoted.

The Hidden Costs: What Sits Between Gross Profit and Real Contribution Margin

Let's break down the cost blocks that eat into gross profit:

1. Marketing Cost per Order

Google Ads, Meta Ads, influencers, SEO content — these costs are rarely broken down to the product level. Yet they vary enormously: a niche product with little competition might have EUR 3 in customer acquisition cost (CAC), while a competitive mainstream product sits at EUR 15 or more.

One example that should give the industry pause: Websale reports cases with EUR 80 customer acquisition cost — for customers who order once for EUR 45 and never return. This isn't an extreme case. It's everyday reality in many shops that don't measure CAC at the product level.

2. Fulfillment and Shipping

Picking, packing, shipping costs, packaging materials. For small, lightweight items, these costs weigh relatively heavier. A product with EUR 9.90 in merchandise value and EUR 4.50 in shipping costs may still look acceptable in gross profit — but fulfillment costs wipe out the margin entirely.

3. Returns

The silent profit killer in German e-commerce. According to the EHI Retail Institute, a return costs up to EUR 20 per item — including return shipping, quality inspection, reconditioning, and depreciation. For apparel, return rates sometimes exceed 50%. Yet only 7.3% of retailers use AI in returns management. Most don't even have the data to allocate return costs at the product level.

4. Payment Costs

Credit card, PayPal, Klarna, instant transfer — each payment method has different fees. PayPal charges up to 2.49% plus a EUR 0.35 fixed fee per transaction. On a EUR 30 item, that's nearly EUR 1.10. Across thousands of orders, it adds up — and is almost never tracked at the product level.

5. Customer Service

Certain products generate disproportionately many support tickets. A technical product with poor instructions can cause EUR 5 to 10 in customer service costs per sale — a figure that never appears in standard reports.

Example Calculation: What a T-Shirt Really Earns

Let's take the T-shirt from above and do the honest maths:

From EUR 21.53 in gross profit, we're left with EUR 1.65 in real contribution margin. That's a margin of 4.9% on net revenue — instead of the 64% the dashboard suggests.

And this is still a profitable product. Change the return rate to 55% or marketing costs to EUR 9, and the T-shirt becomes a loss-maker.

Why This Calculation Is So Difficult in Practice

The problem isn't the maths. The formula is simple. The problem is that the data lives in different systems:

• Revenue and COGS: Shopware, Shopify, ERP
• Marketing costs: Google Ads, Meta Business Manager, CRM
• Fulfillment costs: Logistics system, inventory management
• Returns: Returns portal, ERP, sometimes spreadsheets
• Payment costs: Payment service provider, accounting
• Customer service: Ticket system, helpdesk

For a real contribution margin calculation per product, you need to merge these six to ten data sources, normalise them, and link them at the item level. Manually, that's a project of weeks — and by the time you're done, the numbers are outdated.

This is exactly where oneAgent comes in.

How oneAgent Makes the Real Contribution Margin Visible

oneAgent connects directly to your existing systems — via 550+ connectors, including native integrations for Shopware and Shopify. No data migration, no data warehouse required upfront. Your data stays where it is.

Once sources are connected, you can query the contribution margin in natural language:

"Show me the contribution margin per product after all variable costs — sorted by margin."

"Which ten products have the lowest contribution margin after returns?"

"How does the contribution margin per item differ between Google Ads and organic traffic?"

"Show me the contribution margin per product by channel — split by Google Shopping, Meta, and direct access."

oneAgent translates these questions into the necessary database queries, automatically joins the sources, and delivers results in seconds. An automatic verification layer checks every answer against your actual data — no hallucinations, no estimated values.

In concrete terms, this means:

• Product-level decisions: Which items belong in the Google Shopping budget, which don't?
• Returns optimisation: Which products drive return costs? Is it the product, the product page, or the audience?
• Marketing allocation: Allocate budget to products with the highest real contribution margin — not the highest revenue.
• Assortment management: Identify loss-makers before they drag down your results.

From Revenue Dashboard to Profitability Cockpit

The industry is shifting. EBITDA margins are becoming more important than GMV growth. Investors and CEOs no longer ask "How much revenue?" but "How profitable?"

But you can only manage profitability if you measure it. And you can only measure it if your data comes together.

Most BI tools require a data engineering team spending weeks building pipelines. oneAgent does it in hours instead of weeks — because the connectors are pre-configured and queries work in natural language. No SQL. No Python. No agency.

This aligns with a trend we're seeing across the industry: data analytics is being democratised. Not just data analysts should have access to insights, but CEOs, category managers, and marketing directors — the people who make the decisions.

Three Things You Can Do This Week

You don't need to overhaul your entire reporting right away. But you can start immediately:

1. Identify your top 10 items by revenue — and manually check how high the gross profit really is after returns and marketing. Often a sample is enough to reveal the gap between dashboard and reality.

2. Calculate your average return costs per item — not as a flat rate, but by category. Apparel, electronics, and furniture have entirely different profiles.

3. Ask your finance team whether marketing costs are allocated at the product level. In most companies, the answer is no. That's the starting point for better steering.

When you realise that manual calculation is too complex or too slow, try oneAgent free for 14 days. Connect your data sources and ask the questions your dashboard can't answer today.

Conclusion: Profitability Starts with Visibility

The real contribution margin per item is not optional — it's essential. In a market growing at just 3.2%, success isn't determined by revenue but by efficiency. If you don't know your most profitable products, you're optimising blind.

The data already exists in your systems. It just needs to be brought together.

Try oneAgent free for 14 days — no credit card required.