Most sellers only track revenue and miss costs. Learn contribution profit: subtract COGS, shipping, returns, ad spend, and app fees to see your real bottom line per SKU, per channel, per customer.
StoreWiz Team
Jan 14, 2026 · 13 min read
TL;DR
Revenue is not profit. True ecommerce profitability uses Contribution Profit: Revenue − COGS − Shipping − Returns − Ad Spend − App Fees − Transaction Fees = what you actually keep. Most sellers doing $100K/month in revenue are keeping $8K–$15K. This guide shows you how to calculate your real number, find the hidden costs eating your margins, and analyze profitability per SKU and per channel.
There's a dangerous moment in every ecommerce business. It usually happens somewhere between $30K and $100K in monthly revenue. Sales are growing, orders are flowing, and the Shopify dashboard shows an impressive top-line number.
Then you check your bank account. The money isn't there. Or worse — it's going backwards. You're doing $80K in revenue but somehow have less cash than when you were doing $30K.
This is the vanity revenue trap, and it catches most ecommerce sellers at least once. This guide will help you escape it by teaching you how to calculate true profitability — not the Shopify dashboard version, but the bank account version.
Revenue is the most visible number in your business and the most misleading. Here's why it lies:
The Reality Check
Industry data shows that the average ecommerce net profit margin is 10%. That means a store doing $100K/month in revenue keeps roughly $10K. Many sellers are below this — especially those in the $30K–$80K range who are scaling ad spend without tracking true contribution margin.
Contribution Profit is the metric that tells you the truth. It answers one question: “After every direct cost is paid, how much money did this sale (or product, or channel) actually contribute to my business?”
The Formula
Gross Revenue
− Cost of Goods Sold (COGS)
− Shipping & Fulfillment Costs
− Returns & Refunds
− Advertising Spend
− App & SaaS Fees
− Payment Processing & Transaction Fees
= Contribution Profit (True Profit)
Let's break down each cost line so you know exactly what to include.
COGS is the landed cost of your product — what you paid to have it in your warehouse, ready to ship. This includes:
Common mistake: Many sellers calculate COGS as just the purchase price. If your product costs $8 from the factory but $2.50 in freight, $0.80 in packaging, and $0.40 in 3PL pick-and-pack fees, your true COGS is $11.70 — 46% higher than your naive calculation.
Outbound shipping to the customer is one of the biggest margin killers in ecommerce. Include:
Benchmark: Shipping typically costs 8–15% of revenue for DTC brands. If you offer free shipping (and you probably should — 79% of consumers expect it), this comes directly out of your margin.
Returns cost more than the refund amount. The true cost of a return includes:
Benchmark: The total cost of processing a return is typically 15–30% of the original product price. On a $50 item, a return might cost you $10–$15 in total expenses beyond the refund itself.
Your total ad spend across all paid channels. Include:
Benchmark: Most DTC brands spend 15–30% of revenue on advertising. If you're above 35%, you're likely over-spending relative to your margins — unless your CLV math supports it with high repeat purchase rates.
This is the cost category most sellers dramatically underestimate. The average Shopify store runs 6–12 paid apps. Common ones:
| Category | Typical App | Monthly Cost |
|---|---|---|
| Email Marketing | Klaviyo | $150–$700 |
| Reviews | Yotpo / Judge.me | $0–$299 |
| Subscriptions | Recharge | $99–$499 |
| Customer Support | Gorgias | $60–$750 |
| Analytics | Triple Whale / Lifetimely | $129–$479 |
| Upsells | Zipify / ReConvert | $49–$199 |
| SMS Marketing | Postscript / Attentive | $100–$500 |
| Inventory | Inventory Planner / Stocky | $79–$299 |
| Total App Stack | $666–$3,725/month | |
Add your Shopify plan ($39–$399/month) and any other SaaS tools (project management, accounting, design). Many growing stores spend $1,000–$2,000/month on software alone. At $100K revenue, that's 1–2% of revenue just on apps. Platforms like StoreWiz consolidate many of these tools into a single platform, cutting SaaS costs by 60–80%.
Every sale has a processing cost that most sellers forget to factor in:
Benchmark: Transaction fees typically consume 2.5–3.5% of revenue on Shopify and 15–30% of revenue on Amazon (referral + FBA combined). This is why multi-channel profitability analysis is essential — a product that's profitable on Shopify might be break-even on Amazon.
Let's put the Contribution Profit framework into practice with a realistic example. Meet a DTC skincare brand doing $100K/month in revenue.
| Cost Line | Amount | % of Revenue |
|---|---|---|
| Gross Revenue | $100,000 | 100% |
| COGS (landed cost @ 35%) | −$35,000 | 35% |
| Shipping & Fulfillment | −$11,000 | 11% |
| Returns & Refunds (12% return rate) | −$8,400 | 8.4% |
| Advertising (Meta + Google) | −$22,000 | 22% |
| App & SaaS Fees | −$1,800 | 1.8% |
| Transaction Fees (2.9% + $0.30) | −$3,350 | 3.35% |
| Contribution Profit | $18,450 | 18.45% |
This store keeps $18,450 out of every $100,000 in revenue. That's the owner's salary, reinvestment budget, and emergency fund — combined. And this doesn't even include fixed overhead like rent, insurance, accounting, or payroll if you have employees.
Now here's where it gets interesting. That 18.45% is the blended average. But not every product and not every channel has the same margin.
Most ecommerce businesses follow the 80/20 rule: 20% of your SKUs generate 80% of your profit. The dangerous corollary: some of your SKUs are actually losing money on every sale.
Export your sales data by SKU
Pull the last 90 days from Shopify. You need: SKU, units sold, revenue, and cost per unit. Include variant-level data if you sell the same product in different sizes or colors.
Calculate true landed cost per SKU
Include product cost, packaging, inbound shipping, and storage. A product that costs $8 from the factory might cost $11.50 landed.
Add per-SKU fulfillment costs
Heavier and larger items cost more to ship. A 2 oz serum ships for $4. A 16 oz bottle ships for $8. This changes margin math dramatically.
Apply per-SKU return rates
Not all products have the same return rate. Your sizing-dependent products might have 25% returns while your one-size accessories have 5%.
Allocate ad spend by SKU
If you run SKU-specific ads, assign the spend directly. For brand campaigns, allocate proportionally by revenue contribution.
Rank SKUs by contribution margin
Sort by contribution margin percentage, not total revenue. Your best-selling product might have the worst margin. Your hidden gem might be a mid-volume product with 40% contribution margin.
Example: SKU-Level Insight
A skincare brand discovered that their best-selling moisturizer ($45 retail, 3,000 units/month) had a 12% contribution margin because of high ad spend and a 18% return rate. Their lesser-promoted serum ($62 retail, 800 units/month) had a 34% contribution margin because it sold primarily through email marketing and had a 4% return rate. Shifting ad budget from the moisturizer to the serum increased total monthly profit by $4,200.
Selling on multiple channels is smart for revenue diversification. But not every channel is equally profitable. Here's a typical comparison for the same product:
| Cost Line | Shopify DTC | Amazon FBA | Wholesale |
|---|---|---|---|
| Retail Price | $50.00 | $50.00 | $25.00 |
| COGS | −$12.00 | −$12.00 | −$12.00 |
| Shipping/Fulfillment | −$5.50 | −$7.20 | −$1.00 |
| Platform/Transaction Fees | −$1.75 | −$7.50 | −$0.00 |
| Ad Spend (allocated) | −$11.00 | −$8.00 | −$0.00 |
| Returns (estimated) | −$3.00 | −$5.00 | −$0.50 |
| Contribution Profit | $16.75 | $10.30 | $11.50 |
| Contribution Margin | 33.5% | 20.6% | 46.0% |
Same product, wildly different profitability. Shopify DTC gives you the best margin per dollar of revenue. Wholesale has the highest percentage margin but at half the revenue per unit. Amazon falls in the middle because of higher fees and returns.
This doesn't mean you should abandon Amazon. But it means you should understand the true cost of each channel and make allocation decisions with open eyes.
Beyond the obvious cost lines, there are sneaky expenses that quietly erode margins:
Chargebacks and fraud
Each chargeback costs $20–$100 in fees on top of the lost product and revenue. If your chargeback rate exceeds 1%, payment processors will increase your rates or drop you entirely.
Dead inventory carrying costs
Inventory sitting in a warehouse costs money: storage fees, insurance, and the opportunity cost of capital. A $20K dead stock sitting for 6 months costs $2K–$4K in carrying costs alone.
Customer service costs
Every support ticket has a cost. Whether you're answering emails yourself (your time has value) or paying staff ($15–$25/hour), support costs $2–$8 per ticket. At 500 tickets/month, that's $1,000–$4,000.
Discount and coupon leakage
Active coupons floating around the internet (via sites like Honey or RetailMeNot) mean customers who would have paid full price get a discount. The average ecommerce store loses 1–3% of revenue to unintended coupon usage.
Owner's time
If you're working 60 hours/week on a business that generates $10K/month in profit, you're earning roughly $38/hour. A senior ecommerce manager makes $40–$60/hour. Make sure your profit calculations account for the value of your time.
Pull last month's data and calculate your actual number. Don't estimate — use real numbers from your accounting, Shopify, and ad platforms. Most sellers are shocked by the result.
List every paid app and SaaS tool. For each one, ask: “Would revenue noticeably drop if I cancelled this tomorrow?” If the answer is no, cancel it. Most stores can cut 30–40% of their app spend without impact.
Run the per-SKU profitability analysis. If a SKU has negative contribution margin, either raise the price, reduce its ad spend, or discontinue it. Fewer SKUs = lower complexity costs.
Pause any campaign with a ROAS below 2x (below 3x if your margins are thin). Shift budget to your top 3 performing campaigns. Most stores can cut 15–25% of ad spend while maintaining 90%+ of ad-attributed revenue.
Every 1% reduction in return rate drops straight to your bottom line. Better product photos, sizing guides, video demos, and review photos are the highest-impact investments. Some brands use AI to generate personalized size recommendations.
If you're ordering consistently, negotiate volume discounts. Even a 5% COGS reduction on $35K of monthly product costs saves $1,750/month — that's $21K/year straight to profit.
Manual spreadsheet analysis works once. Automated dashboards work every day. Set up a system that calculates contribution profit in real time across all channels and SKUs. StoreWiz pulls in data from Shopify, Amazon, and ad platforms to calculate per-SKU and per-channel contribution profit automatically.
Key Takeaways
The average ecommerce net profit margin is around 10%. Well-run DTC brands targeting 15–20% is realistic. Above 20% is excellent and usually indicates strong brand loyalty, low return rates, and a diversified customer acquisition mix. Below 5% means you're vulnerable to any cost increase wiping out profitability.
Amazon FBA profitability requires accounting for referral fees (8–15%), FBA fulfillment fees ($3–$8+ per unit), storage fees (monthly and long-term), PPC ad costs, and Amazon's higher return rate (typically 2–3x higher than DTC). Use Amazon's FBA Revenue Calculator as a starting point, then add your PPC costs and actual return rate to get the true number.
Not always. Some products serve as loss leaders that bring in customers who then buy profitable items. Others have high CLV even if the first purchase is break-even. Before cutting a SKU, check: (1) Does it drive repeat purchases? (2) Is it frequently bought with high-margin products? (3) Can you make it profitable by raising the price or reducing costs? If the answer to all three is no, discontinue it.
Full Contribution Profit analysis: monthly at minimum. Per-SKU profitability: quarterly. Per-channel profitability: quarterly. App stack audit: quarterly. If you have automated dashboards, check the high-level contribution margin weekly and investigate any drops immediately.
Contribution margin includes only variable costs that scale with revenue (COGS, shipping, ads, transaction fees). Net profit margin includes everything — fixed costs like rent, salaries, insurance, and equipment. Contribution margin tells you if your business model works. Net profit margin tells you if your business is actually making money after overhead.
Written by StoreWiz Team
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The StoreWiz team writes about ecommerce automation, AI operations, and growth strategies for modern online sellers. Our insights come from building technology that helps brands scale without scaling headcount.
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