Break-even ACoS is your contribution margin before advertising, measured on the same revenue basis as the ad sales denominator. It is the advertising share that would use all that contribution. It does not cover fixed overhead unless you explicitly include an allowance for it.

Start with the right inputs

For one order, record revenue, product cost, marketplace and fulfilment fees, shipping you pay, discounts and expected returns cost. Keep VAT or sales tax treatment consistent with the revenue used in the advertising report. Do not subtract a fee twice if it is already included in another cost field.

Input	What to record
Revenue per order	The revenue basis used in your comparison
Product cost	Landed product cost attributable to the order
Selling and fulfilment costs	Applicable fees and shipping
Other variable costs	Discounts, expected returns and other order-related costs
Desired contribution after ads	An amount or a percentage of the same revenue

Calculate break-even and target ACoS

Contribution before ads = Revenue - Variable costs
Break-even ACoS = Contribution before ads / Revenue
Target ACoS = (Contribution before ads - Desired contribution after ads) / Revenue

Hypothetical example: revenue is £40; product cost £12; marketplace fees £6; fulfilment and shipping £5; other variable costs £1. Total costs are £24 and contribution before ads is £16. Break-even ACoS is £16 / £40 = 40%.

If you want £6 contribution after ads, affordable advertising is £10 per order. Target ACoS is £10 / £40 = 25%, equivalent to ROAS 4.0. At 40% ACoS, this order leaves no contribution toward fixed overhead; at 25%, it leaves £6 under the stated assumptions.

Test a price change before applying the old target

Suppose revenue falls to £36 while the illustrative costs remain £24. Contribution falls to £12 and break-even ACoS becomes 33.33%. To retain £6 after ads, the target becomes £6 / £36 = 16.67%. In a real account, recalculate percentage-based fees too; fixed costs here are an explicit simplifying assumption.

A discount may improve conversion, but do not assume the improvement. Evaluate the new margin and observed conversion separately.

Translate the target into an affordable CPC

With £40 revenue, an assumed 8% order conversion rate and 25% target ACoS:

Affordable CPC = 40 × 0.08 × 0.25 = £0.80

This is an expected-value estimate, not a guarantee per click. Placement adjustments and dynamic bidding affect the bid used in auctions, so distinguish the economic CPC estimate from the entered bid. Amazon bidding guide.

Use this manual worksheet

Paste the tab-separated text into a spreadsheet. Replace the example inputs and calculate totals using the formulas above.

Revenue	Product_cost	Fees	Fulfilment_shipping	Other_variable_costs	Desired_contribution
40	12	6	5	1	6

For a mixed catalog, calculate product-level economics or a revenue-weighted contribution margin. An unweighted average of product margins can misstate how much advertising the actual sales mix can support.

What if contribution is zero or negative?

There is no positive break-even advertising allowance under those economics. Resolve the economics or explicitly approve a bounded loss-making objective. If revenue is zero or missing, do not divide; mark the result unavailable.

Why does the calculator differ from my account ACoS?

The calculator is an economic threshold. Account ACoS is observed spend divided by attributed sales, potentially with different product and time scopes. Verify attribution definitions, then use the ACoS calculator with your own inputs.

Related Arctavia resources

Use these supporting pages to compare Amazon PPC operating models and implementation choices.

• Amazon Ad Rejections: Check Claims, Images and Destinations
• Amazon Ads ACoS Suddenly Increased: What to Check First
• Amazon Ads ML Bid Review: Guardrails Before Aggression
• Amazon PPC Automation: Data, Decisions and Operating Controls
• Amazon PPC Automation Migration Checklist
• Amazon PPC Automation vs Agency: Which Operating Model Fits Better?