How to Set a CAC Target From Your Margin and Payback, Not From a Benchmark

A customer acquisition cost (CAC) target pulled from a benchmark article is a guess wearing someone else's margin. It assumes their shipping costs, their return rate, their repeat purchase behaviour and their appetite for cash burn are close enough to yours to matter. They almost never are. Your target CAC should come from your own contribution margin, your own first order value and the payback window your cash position can actually fund.

Why a borrowed benchmark gives you the wrong number

Benchmarks tell you what other brands paid, not what you can afford to pay. Two brands in the same category can have wildly different gross margins because of sourcing, different average order values (AOV) because of bundling, and different repeat rates because one has a subscription hook and the other doesn't. Average all that together into one "CAC should be under A$X" figure and you've built a target that fits nobody.

My read is that benchmarks are useful for sanity checking after you've built your own number, not for setting it in the first place. If your calculated target is five times the category average, that's worth questioning. If it's just a bit different, it's probably correct, because your business is a bit different.

The arithmetic: contribution margin before anything else

Start with contribution margin, which is what's left of a sale after the costs that scale with each order (cost of goods, shipping, payment processing, return provision). This is different from gross margin on a profit and loss statement, because it strips out the variable costs that disappear if you don't make the sale.

Here's a toy example, illustrative numbers only, in Australian dollars (A$):

• AOV: A$80
• Gross margin before shipping and payments: 55% (A$44)
• Outbound shipping cost: A$8
• Payment processing (roughly 2% plus a fixed fee): A$2
• Returns provision: A$2
• Contribution margin on the first order: A$32

That A$32 is the most a brand in this example can spend on acquisition and still break even on order one. Most brands can't, and shouldn't try to, because the real question is what happens over the next 12 months, not just the first transaction.

Why payback window changes the answer, not just the ceiling

Say this brand's data shows a customer who makes a first purchase typically places 1.6 orders in the following 12 months, each with roughly the same A$32 contribution. That's an expected 12-month contribution per customer of about A$83 (the first order plus 0.6 of a repeat order, since 1.6 total orders includes the first).

Now the target CAC depends entirely on how fast you need that money back:

• At a 1-month payback target, you can only count the first order's contribution. Target CAC sits near A$32, maybe a little under to leave margin for error.
• At a 6-month payback target, if the data shows most of that repeat behaviour lands within six months, you can count a larger share of the 12-month figure, perhaps A$60 to A$70, and your target CAC rises accordingly.
• At a 12-month payback target, you can use close to the full A$83, assuming the business can carry the cash gap that long.

Same brand, same unit economics, three different acceptable CAC figures. The spread isn't a modelling error, it's the honest cost of waiting longer to get paid back. A founder with six months of runway and no credit facility has a very different answer to a founder with a credit line and investor cash sitting idle.

Why cash, not ambition, picks the payback window

This is where a lot of CAC targets quietly fall apart. The founder sees that a 12-month payback window lets them bid more aggressively and compete harder for customers, so they set the target as if they have a year to wait. But if the business needs the cash back inside two or three months to fund inventory for the next order cycle, that 12-month target CAC is unaffordable in practice, even though it's correct on paper.

Payback window should be set by your cash conversion cycle, your access to working capital and how much of your own money you're willing to have tied up in customers who haven't fully paid you back yet. Ambition sets a wish list. Cash sets a budget. If those two numbers disagree, the lower one wins.

The trap of blended revenue in a new-customer CAC

A common mistake: a brand looks at total revenue per customer across its whole base, including loyal repeat buyers who've been purchasing for years, and uses that blended figure to justify a high CAC on new customer acquisition. The problem is that new customer behaviour in month one looks nothing like a long-time customer's lifetime average. You're funding today's acquisition cost with tomorrow's hoped-for loyalty, and if the repeat rate assumption is wrong, there's no going back and un-spending that media budget.

A cleaner approach is a short checklist before setting the number:

• Pull contribution margin on a first order specifically, not blended margin across the base
• Segment repeat rate and timing by cohort, not an all-time average
• Decide your payback window from cash position first, ambition second
• Calculate target CAC at that window, then compare to any benchmark, not the other way around

Key takeaways

Contribution margin, not gross margin, is the starting number. Strip out shipping, payment costs and return provisions before you decide what you can afford to spend.

Payback window is a cash decision, not a growth decision. The same unit economics produce a different target CAC depending on how fast you need the money back.

Blended lifetime revenue is the wrong input for a new-customer target. Use first-order and early-cohort data, because that's the money actually funding the next round of acquisition.

Benchmarks are a sanity check, not a starting point. Build your number first, then see if it's in a sensible range for your category.

If you want a second pair of eyes on this arithmetic for your own numbers, that's a conversation worth having with a dtc paid media consultant before you set next quarter's media budget, not after.