How much can you afford to spend on advertising?

Use matching revenue and cost definitions

ACoS is advertising spend divided by advertising-attributed sales. ROAS reverses those terms: advertising-attributed sales divided by advertising spend. Neither metric subtracts product, fulfillment, returns, or overhead costs. A strong-looking revenue multiple can still be unprofitable.

Use the same time window, currency, and attribution definition when comparing campaigns. Revenue attributed by an ad platform is not necessarily incremental revenue caused by the ad. Customers may have purchased anyway, and multiple platforms may claim credit for the same order.

For planning, estimate how much one advertising-acquired order contributes before advertising. If the basket contains multiple products, use the actual basket margin rather than applying a single product’s percentage to the whole order.

Calculate a ceiling from the $30 order

Assume a $30 order has $20.70 of variable costs before advertising. That leaves $9.30, or 31% of revenue, to cover advertising and whatever contribution you need to retain. All values here are hypothetical and assume one attributed sale corresponds to one completed order.

Spending the entire $9.30 means zero contribution is left for fixed costs or profit. That gives a variable-cost break-even ACoS of 31% and ROAS of about 3.23. Calling it business break-even would be misleading because overhead remains unpaid.

Suppose you want to retain $4.50 per order for overhead and profit. The advertising ceiling becomes $9.30 minus $4.50, or $4.80 per order. That translates into a 16% target ACoS and a 6.25 ROAS. If no feasible campaign can meet that target, revisit the economics or the acquisition strategy.

Translate the order limit into a click limit

A planning CPC ceiling is allowable advertising cost per order multiplied by expected orders per click. With a $4.80 order limit and a 10% conversion rate, the estimated ceiling is $0.48 per click. At a 5% conversion rate, it falls to $0.24.

This is a sensitivity calculation, not an instruction to set every bid at that number. Conversion rates vary by query, placement, device, listing quality, and season. A small sample can produce an unstable rate. Returns, attribution delays, and changes in basket value also affect the result.

Make the test small enough to learn from

Write down a spend cap, a review date, and what would count as success before launching a test. Separate branded searches from discovery campaigns so existing demand does not disguise the cost of finding new customers.

Review settled revenue and contribution alongside platform reporting. A campaign that appears expensive may support repeat purchases, but do not assume that benefit: use observed repeat contribution and the time required to recover the acquisition cost.

When you discount a product or a fulfillment charge changes, recalculate the ceiling. A bid that worked last month may no longer fit the same product. The worksheet lets you compare a base case with a weaker conversion or margin scenario.

• Confirm which sales the platform attributes to advertising.
• Track contribution after advertising, not only impressions and sales.
• Keep a record of assumptions and changes so a result can be reproduced.
• Use verified customer economics before justifying losses with lifetime value.