Most e-commerce sellers know their revenue and have a rough sense of their net income. What most sellers cannot tell you is what it costs to acquire each order on each channel, which SKUs are profitable after advertising, or whether a channel that looks healthy in aggregate is subsidizing a group of products that should have been discontinued.
Advertising spend is often one of the largest controllable expenses in an e-commerce operation. It is also the most commonly misread in the books. This guide covers how advertising costs are structured, why standard bookkeeping misrepresents their impact, and how to set up your books and reporting to see channel-level and SKU-level profitability after advertising.
What advertising spend includes
For Canadian e-commerce sellers, advertising spend typically includes the following:
Amazon Sponsored Products, Sponsored Brands, and Sponsored Display. Pay-per-click campaigns run within Amazon’s advertising platform. Advertising charges are tracked separately from marketplace selling fees and appear on Amazon Advertising billing reports. Depending on account settings and marketplace, charges may be billed to a payment method on file or offset against seller balances.
Meta advertising (Facebook and Instagram). Cost-per-click or cost-per-impression campaigns driving traffic to a Shopify store or other storefront. Charged directly to a credit card or Meta ad account and invoiced separately.
Google Ads. Search, Shopping, and Performance Max campaigns. Billed to a Google Ads account linked to the seller’s payment method.
TikTok Shop and other platform ads. In-platform ads driving to TikTok Shop listings. Billed through TikTok’s advertising platform.
Influencer and affiliate commissions. Payments to content creators or affiliates for sales they drive. These may be tracked through a platform like a third-party affiliate network or managed manually.
Email marketing platform costs. Platforms used for promotional email sequences. These are often classified as marketing or advertising expenses for internal profitability analysis, although accounting treatment varies between businesses.
For most sellers, Amazon PPC, Meta ads, and Google Ads account for the bulk of advertising spend, with the relative weighting depending on which channels they sell on.
Why the standard bookkeeping view is incomplete
The most common approach to advertising spend in e-commerce bookkeeping is to record it as a single operating expense line and compare it to total revenue. That tells you what percentage of revenue went to advertising in aggregate. It does not tell you:
- What it cost to acquire a sale on Amazon versus Shopify
- Which products generated profitable orders after ad spend and which did not
- Whether a campaign that increased revenue also increased profit
When all advertising costs are pooled under one expense account, the profitability view is revenue minus total costs, with advertising as one of many operating expenses. That view is accurate for the overall business but is not actionable at the level where pricing and inventory decisions are made.
A seller who averages a 30% gross margin across 50 SKUs, spends 20% of revenue on advertising, and looks at the combined result sees a 10% net margin. The same seller, looking at SKU-level contribution margins after advertising, may find that 15 of those SKUs are generating negative contribution margins, subsidized by the other 35. The combined view obscures the decision.
Gross margin, contribution margin, and why the distinction matters
Gross profit is revenue minus the cost of goods sold (COGS). Gross margin is gross profit expressed as a percentage of revenue. For an e-commerce seller, COGS should include full landed cost per unit (purchase price, freight, duties, brokerage). It does not include advertising, fulfillment fees, or marketplace commissions.
Contribution margin is revenue minus COGS minus variable costs directly attributable to the sale. For e-commerce, the most meaningful variable costs to subtract are marketplace fees (Amazon referral fee, Shopify payment processing, etc.), fulfillment costs (FBA fees, third-party logistics fees, shipping), and advertising spend directly attributable to those sales.
Contribution margin answers the question: does this product generate a positive contribution margin after paying for the inventory, the cost of selling it, and the cost of acquiring the customer? Gross margin does not answer that question because it excludes the cost of selling.
A product with a 40% gross margin and a 30% advertising spend rate has a contribution margin of roughly 10% before fulfillment and marketplace fees. After those costs, it may be negative. That SKU is not profitable at current advertising spend, regardless of what the gross margin says.
Amazon: ACOS, TACOS, and what they do not tell you
Amazon sellers commonly use two metrics to evaluate campaign performance:
ACOS (Advertising Cost of Sale) is the ratio of advertising spend to revenue generated directly by those ads. It is the core efficiency metric for Amazon PPC campaigns.
ACOS = Ad spend / Revenue from ads
If a campaign spent CAD $200 and generated CAD $1,000 in attributed revenue, ACOS is 20%.
ACOS measures efficiency within a campaign. It does not measure whether the underlying product is profitable at that ad spend level, because it does not account for COGS, FBA fees, or marketplace referral fees.
TACOS (Total Advertising Cost of Sale) is advertising spend divided by total revenue, not just ad-attributed revenue. TACOS accounts for the fact that brand awareness from ads drives organic sales that do not appear as ad-attributed.
TACOS = Ad spend / Total revenue
A product with ACOS of 30% and TACOS of 12% is generating meaningful organic velocity alongside its paid traffic. A product where ACOS and TACOS are nearly equal has almost no organic sales; every unit sold is effectively acquired through paid advertising.
The limitation of both metrics is that they measure advertising cost as a percentage of revenue, not as a contribution to profitability. A seller can have an ACOS of 15% on a product that still loses money on every unit sold because COGS and FBA fees leave no margin to cover advertising.
To evaluate true profitability at the product level, you need to combine ACOS or TACOS data with COGS and fulfillment costs. The question to answer is: at current ad spend, after accounting for the cost of the goods and the cost of fulfilling and selling them, is this product generating a positive return?
Maximum sustainable ACOS. Every SKU has a maximum ACOS it can support before advertising produces a negative contribution margin. Above that threshold, advertising adds revenue but destroys contribution margin. If a product has a 45% gross margin, fulfillment costs equal to 15% of revenue, and a 10% Amazon referral fee, the remaining margin before advertising is 20% of revenue. An ACOS above 20% on that product means advertising is costing more than the product earns after COGS and selling costs. Calculating this threshold per SKU and comparing it to actual ACOS from Amazon’s campaign reports is a practical way to identify which products are being advertised at a loss, regardless of how the campaigns look in isolation.
Customer acquisition cost and channel comparison
Customer acquisition cost (CAC) measures the total cost of acquiring one paying customer, including all advertising spend attributed to that acquisition. It is most useful for Shopify and direct-to-consumer channels where repeat purchase behaviour is meaningful.
CAC = Total ad spend / Number of new customers acquired
For a channel where customers buy once and do not return, CAC needs to be compared directly to the profit on that first order. If acquiring a customer costs CAD $25 and the first order generates CAD $18 in contribution margin, the channel is losing money on each new customer acquired.
For a channel where customers return, the lifetime value of the customer can justify a higher initial CAC. A seller who spends CAD $25 to acquire a customer who then purchases four times over two years, generating CAD $18 in contribution margin each time, has a positive overall return even though the first order appears unprofitable.
Multi-channel sellers often find that the economics differ substantially between Amazon and their own Shopify store. Many sellers find that Amazon generates higher order volume but lower per-order margins due to referral fees and advertising costs, while Shopify offers greater control over customer relationships and repeat purchase rates. The actual economics depend on the seller’s product category, advertising strategy, and customer base. Comparing CAC and contribution margin across channels requires that advertising spend and order data be tracked separately by channel.
How to track advertising spend by channel
The accounting setup that makes channel-level profitability visible requires class or category tracking in your accounting software.
Separate expense accounts or classes for each advertising channel. Rather than recording all advertising in a single “Advertising” account, set up sub-accounts or classes for Amazon Advertising, Meta Advertising, Google Ads, and any other active channels. This lets you pull a channel-level expense report that shows what you spent on each platform in any period.
Link advertising spend to revenue by channel. Advertising spend should be linked to the channel it is intended to support. Amazon Advertising is typically associated with Amazon sales, while Meta and Google campaigns are often associated with Shopify or other direct-to-consumer channels, though some brands use off-platform ads to drive Amazon traffic as well. If revenue is tracked by channel (which it should be, since Amazon, Shopify, and other platforms settle separately), advertising spend tracked by channel can be compared to revenue by channel.
Per-SKU or per-product-group advertising. Amazon’s advertising reports can be exported at the campaign and ASIN level, showing spend and attributed revenue per product. For a seller running multiple SKUs with separate campaigns, this data enables SKU-level contribution margin calculations when combined with COGS and FBA fee data.
Most sellers do not need this level of detail for every product. But for the top 20% of SKUs by revenue, and for any SKU where margin appears thin, per-product advertising data is the most direct way to identify whether the product is profitable at current advertising intensity.
Multi-channel sellers: channel contribution margin
A seller running Amazon and Shopify simultaneously with active advertising on both is operating two distinct margin structures. Reporting them together produces a combined margin that obscures the performance of each channel.
A simple channel-level contribution margin report for a period would show:
| Amazon | Shopify | |
|---|---|---|
| Revenue | $80,000 | $35,000 |
| COGS | ($32,000) | ($14,000) |
| Marketplace fees | ($14,400) | ($3,150) |
| Fulfillment | ($9,600) | ($5,250) |
| Advertising | ($12,000) | ($7,000) |
| Contribution margin | $12,000 | $5,600 |
| Contribution margin % | 15% | 16% |
The combined view would show revenue of $115,000 and a combined contribution margin of $17,600, or about 15.3%. The channel-level view shows similar margin percentages but substantially different absolute dollar contribution and very different advertising intensity ($12,000 on $80,000 Amazon revenue vs. $7,000 on $35,000 Shopify revenue).
Decisions about where to invest advertising dollars, whether to expand one channel relative to another, and how to price across channels all benefit from this level of visibility.
Common mistakes
Recording all advertising as a single line item. When advertising spend is pooled, channel-level profitability analysis requires going back to source documents to reconstruct which spend belonged to which channel. Setting up channel-level accounts takes minimal effort at the start and avoids significant reconstruction work later.
Evaluating campaigns by ACOS alone without reference to product economics. An ACOS that looks acceptable may still be generating negative contribution margin if COGS and fulfillment costs are high. ACOS tells you about campaign efficiency, not product profitability.
Treating ad spend as a fixed cost. Advertising spend is variable and discretionary in a way that rent or payroll is not. A seller who reduces advertising by 20% and loses 15% of revenue has made a profitable decision if the contribution margin on that revenue was thin. Recognizing advertising as a variable cost that can be scaled up or down by channel or product is part of running an advertising-aware operation.
Not separating advertising from promotional credits. Amazon occasionally issues advertising credits, and some campaigns generate credits or rebates. These should be recorded separately from cash ad spend. Including credits in the advertising expense total without netting them out overstates the expense.
Waiting for the annual income statement to review ad spend. Advertising spend should be reviewed at least monthly by channel. If a campaign is generating negative contribution margin, the sooner it is identified the sooner it can be adjusted. An annual review catches problems after twelve months of overspending.
Related Guides
- Multi-Channel Reconciliation: Amazon, Shopify, and Walmart covers how to reconcile settlement payouts and revenue across platforms, which is the foundation for channel-level profitability reporting.
- Landed Cost for Canadian E-Commerce Sellers covers how to calculate accurate COGS per unit, which is the input needed for contribution margin calculations.
- Inventory as a Cash Flow Problem covers how inventory purchasing and ad-driven demand changes interact with cash flow.
Scope of This Guide
This guide covers how to track and analyze advertising spend to assess true profitability at the channel and SKU level for Canadian e-commerce sellers. It does not cover:
- Amazon PPC campaign structure, bidding strategies, or keyword targeting
- Meta or Google Ads campaign setup or optimization
- Attribution modelling for multi-touch customer journeys
- GST/HST on advertising purchased from non-Canadian platforms such as Meta and Google (many Canadian sellers are unaware that GST/HST obligations can arise on these purchases; this will be covered in a separate guide)
- Influencer contract structures or performance-based commission arrangements
The goal is for advertising spend to be visible in the books at the level where decisions are made: by channel and, where material, by product. Without that visibility, it is not possible to tell whether an increase in advertising budget is adding profit or just adding revenue.