Choose the CAC Measure That Fits the Decision

Customer acquisition cost (CAC) is the acquisition spend divided by the number of new customers acquired in the same period. It answers: what did it cost to add one customer? Define the spend consistently before comparing periods or channels; the separate question of which costs belong in that spend comes later.

Allowable CAC is a pre-set decision threshold, not an observed result. It is the most you are prepared to spend to acquire a customer under a defined economic rule. Use it to approve, limit or stop a campaign. A CAC calculator can help test the arithmetic behind that threshold without mixing in assumptions about retention or fixed overhead.

First-order CAC compares acquisition spend with new customers whose first order occurred in the period. Use it when deciding whether the initial transaction can support acquisition. Blended CAC uses total defined acquisition spend across channels divided by all new customers, including customers whose source is unattributed. Use it for the store-wide acquisition picture and budget control. Neither measure should quietly add repeat-order revenue, retention forecasts or general overhead; those are separate analyses.

Choose the measure that matches the decision
MeasureWhat it measuresWhen to use it
Allowable CACThe maximum acceptable cost per new customerSet a spending boundary before launching or scaling
First-order CACAcquisition spend per customer on a first orderJudge the economics of the initial purchase
Blended CACTotal defined acquisition spend per new customer across the storeManage overall acquisition efficiency and budget

What belongs in acquisition cost

Acquisition cost should include every cost incurred to win a new customer, not just the amount paid to Meta or Google. Include paid media, affiliate or creator commissions, acquisition-specific agency or freelancer fees, and creative production used for prospecting. Include a first-order voucher or free-shipping subsidy when it is offered specifically to convert a new customer. Do not add product cost, fulfilment, general rent or staff costs here; those belong in the profitability view rather than the acquisition line.

Keep the tax basis consistent. GST is 10% on most goods and services in Australia, and a registered business collects the GST portion, which is one-eleventh of the sale price, according to business.gov.au (Australian Government). If your store can claim GST credits, compare acquisition costs excluding recoverable GST. If GST is not recoverable, include the amount you actually pay. Otherwise, a campaign can appear more expensive simply because one report is GST-inclusive and another is not (Source: business.gov.au (Australian Government)).

There are two useful versions to compare. Cash CAC includes the costs that left the bank during the period, so it suits immediate budget decisions. Fully loaded acquisition cost also allocates relevant agency, creative and software costs, so it suits planning and assessing whether the acquisition model is structurally affordable. Use the CAC calculator to test both views, and connect Shopify with advertising accounts in ORVX when you need store revenue and ad spend in the same currency and reporting context.

Worked example with sample numbers

This example is illustrative. It uses sample numbers for a craft beverages store selling in Australia. They are made up to show the method, they are not a benchmark, and your own figures will differ.

Formula: Ceiling = margin per order x orders per customer / target ratio.

Sample numbers: the most you can pay for a customer
Orders per customerMargin earnedCeiling at a 3:1 target
1.0A$29.10A$9.70
1.5A$43.66A$14.55
2.0A$58.21A$19.40
3.0A$87.31A$29.10

Run the same sum with your own numbers in the free calculator, or browse guides for sellers in Australia and more craft beverages guides.

General information only: tax, duty and import rules change and depend on your situation, so check with an accountant or the official source before acting.

Eligible Shopify stores can see these numbers for their own store through the Founding 10,000 offer.

First-order margin as a ceiling

First-order margin sets the maximum CAC you can tolerate if the first purchase must pay for itself. Start with delivered-order revenue, remove GST where applicable, then subtract product cost and other variable fulfilment costs such as packaging, payment fees and any shipping subsidy. The remainder is the first-order contribution available to acquire that customer.

For illustration only, a delivered order at $110 including GST has $100 of GST-exclusive revenue because GST is one-eleventh of the sale price. If product cost is $42, fulfilment and packaging are $12, and payment fees are $3, the contribution before acquisition is $43. A $43 CAC is therefore the break-even ceiling for that order; a $25 CAC leaves $18 before fixed operating costs. This is a limit, not automatically a sustainable target: rent, wages, software, breakage and other overhead still need funding.

Use gross margin when comparing product or collection economics, and use contribution after variable costs when deciding whether a first-order CAC is financially acceptable. ORVX computes gross profit and margins from a product cost model, and reports contribution after advertising by product and collection. Its CAC calculator can help test the arithmetic, while delivered, returned and cancelled orders should be kept distinct from revenue. The Australian Government states that registered businesses collect GST as one-eleventh of the sale price; GST registration is required at $75,000 or more in GST turnover (Source: business.gov.au (Australian Government)).

How repeat orders change the limit

Repeat orders can raise the sustainable CAC limit, but only when the additional orders produce contribution, not merely revenue. For illustration only, if a new customer contributes $18 after product, fulfilment, payment and other variable costs on order one, then $16 on order two and $14 on order three, the three-order contribution is $48. A CAC of $30 may be unsustainable on first-order economics but viable over that observed customer horizon, leaving $18 to cover fixed costs and profit.

Use the measure that matches the decision. First-order CAC is the right control for testing whether acquisition pays back immediately. Cohort CAC payback is more useful when customers reliably reorder: compare CAC with cumulative contribution after 30, 60 or 90 days, using completed cohorts rather than an assumed lifetime value. If repeat behaviour varies by product, subscription status or acquisition source, use the relevant cohort instead of one store-wide average.

ORVX shows customer-level profitability and repeat behaviour, alongside contribution after advertising by product and collection. That helps separate profitable retention from repeat orders that become unprofitable after discounts or returns. Use the CAC calculator for the initial arithmetic, then validate the limit against your own completed customer cohorts.

Tracking the number by channel

Track three views rather than forcing one CAC figure to answer every question. Blended CAC divides total acquisition cost by all new customers and is the right measure for deciding whether the store’s overall growth is affordable. Channel CAC assigns spend and related acquisition costs to the channel that generated the customer; use it to decide where to scale, reduce or investigate. Platform-reported CAC uses each advertising platform’s own attribution rules, so it is useful for campaign optimisation but should not replace the store-level number.

Keep the period, new-customer definition and attribution window consistent across channels. Compare paid social, search, affiliates, creators and email separately, then reconcile their customers to the blended total. A channel can show an attractive attributed CAC while total store CAC rises if it is claiming customers who would have purchased anyway. ORVX connects Shopify with advertising accounts, keeps store revenue beside ad spend, and reports MER separately from attributed ROAS. Use the CAC calculator for a consistent calculation, then validate decisions against customer-level profitability and repeat behaviour.

Which CAC view should guide the decision?
MeasureUse it forAct when
Blended CACOverall growth affordabilityTotal acquisition economics change
Channel CACBudget allocation by sourceOne channel’s economics diverge
Platform-attributed CACCampaign optimisationCreative, audience or bid performance changes

Sources

How this page was made: drafted with AI from a brief, then checked by automated rules for arithmetic, sources and duplication. The sample numbers were calculated, not reported.