Calculate contribution before advertising
Subtract product cost, packaging, shipping, fulfillment, selling fees and expected unrecovered returns from the selling price. Leave advertising out of this first step. Break-even ACOS = contribution before advertising ÷ selling price × 100. This is before overhead and income tax.
A simple ACOS and ROAS example
If a $20 sale leaves $6 before advertising, the break-even ad allowance is $6 and break-even ACOS is 30%. Break-even ROAS is $20 ÷ $6, or about 3.33. If you want $2 contribution left after ads, the allowance falls to $4, giving a 20% target ACOS and a 5.0 target ROAS.
Turn the allowance into a click-cost limit
Maximum CPC = advertising allowance per order × assumed conversion rate. With a $4 allowance and a 10% conversion rate, the planning limit is $0.40 per click. If conversion falls to 5%, that limit becomes $0.20. The conversion assumption must match the traffic and product being modeled.
Use the result as a guardrail
ACOS is ad spend divided by ad-attributed sales. Total advertising cost of sales uses total sales, including organic revenue. Keep those measures separate. Attribution timing, returns and multi-unit orders can change the result. SKUHarbor’s paid advertising planner lets you test these assumptions alongside target profit and bundle pricing.