The short answer
A break-even target uses all contribution before ads to pay for advertising. To leave a specified share of revenue afterward, reserve that share before calculating the acquisition allowance. Be precise about the label: contribution after ads is not necessarily final net profit.
Calculate a margin-based target
Use contribution margin, not markup. The result covers only your included costs. Inputs stay in your browser. Displayed results are rounded.
Define two margin fractions
Let m be contribution before advertising divided by revenue. Let p be the desired contribution after advertising divided by the same revenue. The advertising allowance as a fraction of revenue is m − p. The model requires positive revenue and m greater than p for a positive ad budget.
Target CPA per order = order revenue × (m − p)
Calculate a target
Illustrative inputs: an order produces $120 in revenue and $72 of non-ad variable costs. Contribution before ads is $48, so m = $48 ÷ $120 = 0.40. Suppose the desired contribution after ads is 15% of revenue, so p = 0.15. The ad allowance is $120 × (0.40 − 0.15) = $30. Target ROAS is 1 ÷ 0.25 = 4×.
At that target, the order leaves $120 − $72 − $30 = $18. The check is $18 ÷ $120 = 15%. Any fixed overhead or other excluded expenses still need to be funded from that $18 or accounted for elsewhere.
Test whether the request is feasible
If the desired post-ad margin equals the pre-ad margin, the model allows no ad spend. If it exceeds that margin, the advertising allowance is negative. No positive-spend ROAS target can satisfy those inputs. Revisit the desired margin, pricing, or costs rather than forcing a plausible-looking result.
Use the correct kind of margin
Do not substitute markup, product-only margin, or a margin using a different tax or refund basis. For a mixed catalog, calculate a revenue-weighted contribution margin from the expected mix. If the costs change with volume, recompute the model rather than treating the original margin as permanent.
Separate planning from delivery
This target states what the economics require; it does not establish that an ad system can deliver it at the desired volume. Compare it with mature historical performance, uncertainty, and available cash. Keep both the required target and actual result visible so a budget discussion does not confuse an aspiration with an achieved return.
Check target feasibility
- Gather: Measure pre-ad contribution margin and specify the share of revenue to retain after ads.
- Produce: Subtract the desired share before taking the reciprocal for target ROAS.
Decision boundary: If the desired share is at least the pre-ad margin, no positive ad budget satisfies the model.
Next reading
Examples are illustrative, not client results or benchmarks. The calculations use the inputs shown; real-world decisions depend on your records and assumptions. Report a correction.