What is your break-even cost per acquisition? Work it out before you scale

Before you increase your ad budget, work out how much you can afford to spend acquiring a new customer. Your break-even cost per acquisition is a ceiling, not a sensible everyday target. Spend right up to it and there is nothing left for profit or a disappointing month.

My recommendation: calculate a media-only ceiling from retained revenue and real costs, then set a lower working target. Do this before scaling either Meta or Google Ads. A platform reporting a cheap conversion does not settle the commercial question.

First, decide what you are acquiring

Google defines average CPA as the amount charged for ad conversions divided by the number of conversions. CPA means cost per action in that definition. The action might be an enquiry or purchase; it is not automatically a new customer.

Even Google's "One" counting setting works per ad interaction and conversion action, not as a universal unique-customer filter. Repeat purchases, separate enquiry actions and existing customers can all make conversion counts unsuitable for calculating customer acquisition cost.

Label three figures separately: media cost per qualified lead, media cost per actual new customer, and full acquisition cost per actual new customer. That last figure includes relevant management fees, sales effort and other acquisition costs, not just platform spend. Delivery costs belong in the contribution calculation below, not in acquisition spend as well.

Use deduplicated customer records from your shop or customer relationship management system. State the cohort, conversion window and attribution rule. Match its acquisition costs to those customers, allowing sales time to mature. For blended acquisition cost, include the relevant spend across channels and count each new customer once. Do not add two platforms' claimed conversions together. Attribution allocates credit; it does not prove every sale was caused by advertising.

Calculate what is available before media

Contribution margin is revenue minus variable expenses. It pays towards fixed costs and profit; it is not net profit itself. For this calculation, use a clearly labelled "contribution before media" subtotal: retained revenue minus product and variable delivery costs. Keep non-media acquisition costs separate so you can see them, and subtract each cost only once.

Start with revenue after discounts and refunds. Deduct product costs, payment charges, packing, shipping subsidies, variable delivery labour and returns processing where relevant. Include sales commissions and paid follow-up in non-media acquisition costs, including work on leads that never buy. Allocate management fees, tracking tools and client-funded creative production to the same scope.

Then reserve a defensible share of fixed overheads. Without that provision, the result is a marginal acquisition ceiling, not a business break-even calculation. A cohort's overhead allocation still does not prove the whole business breaks even.

Media-only break-even budget = cohort contribution before media - non-media acquisition costs - overhead provision.

Working media budget = media-only break-even budget - desired profit - safety buffer. Divide either budget by actual new customers to get its corresponding media CPA. The buffer stays unspent; it is not permission to buy more conversions.

Both examples below are entirely hypothetical, in Australian dollars. They assume GST-registered businesses, taxable sales at 10% GST and eligible input credits. Revenue excludes output GST; costs exclude recoverable GST but retain any non-recoverable amounts. Confirm the correct treatment with your accountant. This is a planning framework, not tailored tax or financial advice.

Ecommerce example: AU$27 breaks even, AU$14 is the target

Suppose a cohort contains 100 actual new customers making their first purchase. Each first order averages AU$110 including GST, or AU$100 excluding GST. An average AU$4 refund allowance leaves AU$96 retained revenue per acquired customer.

Product cost is AU$40, packing and delivery AU$12, payment fees AU$3 and returns processing AU$1. Those costs total AU$56, leaving AU$40 contribution before media per customer, or AU$4,000 across the cohort.

Allow AU$600 for management and AU$200 for assets produced by the client's team or supplier. Reserve AU$500 for overheads. The media-only break-even budget is AU$4,000 - AU$800 - AU$500 = AU$2,700. Divide by 100 new customers: AU$27 media CPA breaks even within this scope.

Now require AU$1,000 profit and leave AU$300 untouched as a buffer. That leaves AU$1,400 for media, giving a working target of AU$14 per new customer. Including the AU$800 non-media acquisition costs, full acquisition cost at that target is AU$22 per customer.

An account showing AU$20 per purchase is not automatically ready to scale. Even if every purchase were a new customer, it would exceed the AU$14 working target despite sitting below break-even. If purchases include returning customers, reconcile the denominator before deciding anything.

Lead-generation example: work backwards from paid jobs

Imagine 100 unique qualified leads in a mature cohort produce 25 completed, paid jobs for new customers: a 25% qualified-lead-to-customer rate. Define "qualified" consistently, for example an eligible prospect in your service area with a suitable job, not every submitted form.

Each job brings AU$1,650 including GST, or AU$1,500 excluding GST. Variable delivery labour, materials and travel cost AU$900, leaving AU$600 contribution before media per customer. This example assumes no refunds; deduct them where they occur. The cohort contributes AU$15,000.

The client's sales team spends AU$15 following up each qualified lead, including unsuccessful ones: AU$1,500. Add AU$1,000 management and reserve AU$1,250 overheads. The media-only break-even budget is AU$15,000 - AU$2,500 - AU$1,250 = AU$11,250: AU$450 per new customer, or AU$112.50 per qualified lead.

Reserve AU$3,750 profit and AU$1,250 buffer. Available working media budget becomes AU$6,250. That gives AU$250 per new customer or AU$62.50 per qualified lead. Full acquisition cost, including management and sales follow-up, is AU$350 per new customer.

The denominators matter. AU$62.50 per qualified lead only maps to AU$250 media CPA while 25% become customers. At a 10% close rate it becomes AU$625 per customer. Recalculate contribution, fee allocations and the budget at that lower customer volume; do not preserve the original ceiling.

Make the scaling decision with mature evidence

If there are no new customers, acquisition cost is undefined, not AU$0. If there are no qualified leads, cost per qualified lead and the qualified-lead close rate are undefined too. Investigate tracking and sales lag before drawing conclusions. A negative available budget means this plan cannot support positive media spend.

Use first-purchase or first-job contribution unless repeat-customer data supports more. Lifetime value should mean verified retained contribution over a stated period, after retention and delivery costs, not imagined future revenue. Even credible repeat-purchase evidence does not remove today's cash-flow constraint.

Scale only when mature cohorts meet the lower target, the next customers look economically comparable and the client can fulfil or follow up more volume. Cap spending at what cash flow can support, even if the calculated budget is higher. If your next customers cost more or buy lower-margin products, revise the model rather than defending the old average.

Use our Meta Ads budget guide or Google Ads budget guide for wider spending decisions, and our Google Ads metrics guide for reporting context. Keep this calculation beside those decisions.

If you cannot reconcile platform conversions with paid new customers, hold the increase. Bring your cost breakdown and mature customer records to a Nexus ads consultancy session to review measurement and campaign decisions. Your team retains final creative production, comments, messages and customer follow-up. Set a defensible ceiling first; scale only when the evidence supports spending below it.