Most founders can tell you how much they spend on ads each month. Fewer can tell you what it actually costs them to land a single paying client. And even fewer understand how important that number actually is. Just over half of marketers know their metrics, so don’t feel bad if you don’t. But it’s time to change that!

Customer acquisition cost (CAC) isn’t just a marketing metric — it’s a key measure of your profitability potential. It affects your margins, your potential growth speed, how much risk you have and how resilient your business is in different conditions. Whether you’re running paid ads, relying on referrals or posting on Instagram when you remember, CAC is always there, shaping the sales and marketing math behind the scenes.

Let’s break down what CAC actually is, why it matters way more than most founders realize and how to think about it in a way that doesn’t make your head spin.

What CAC actually is

At its simplest, CAC is how much it costs you to acquire a new client.

The basic formula looks like this:

Total sales and marketing spend ÷ number of new clients acquired

That includes ad spend, software, agencies, contractors, sales commissions and even your own time if you’re doing sales yourself. If you spent $5,000 on marketing and sales last month and signed 10 new clients, your CAC is $500.

A key thing to remember is that CAC is not just for your ads. Even if you don’t run ads, you still have a CAC. Time spent networking, posting content, sending follow-ups, paying referral fees, investing in funnel automations, hopping on discovery calls and nurturing leads all have a cost.

Why CAC directly impacts your margins

Every dollar you spend to acquire a client comes out of your margin.

If you sell a $2,000 service and it costs you $1,200 to deliver, your gross margin before marketing is $800. If your CAC is $600, your real margin is now $200. If your CAC creeps up to $900, you’re losing money on every sale, even though revenue looks fine.

This is how businesses grow their top line and still feel broke at the end of the month.

Founders often focus on revenue targets without realizing their CAC is silently eating the profit. They’ll say things like “We just need more volume” or “We’ll make it up later with upsells” without actually checking whether the math supports that plan.

If your CAC is too high relative to your pricing and margins, scaling just makes the problem worse, as it just compounds how much you’re losing.

CAC determines how fast you can grow

Growth speed isn’t just about demand; it also relies on having enough cash to invest in that growth.

If it costs you $1,000 to acquire a client and you get paid $1,000 upfront, you’ve just broken even on day one. If it costs you $1,000 to acquire a client and you get paid $250 per month, you’re fronting the cost and waiting four months to recover it.

That’s fine if you’ve planned for it, but dangerous if you haven’t.

High CAC slows growth because it ties up cash and makes it more high-stakes for you to retain those clients. Every new client requires more capital before you see a return. This is why two businesses with the same revenue can feel wildly different to run. One has a low CAC, and cash comes back quickly. The other has a high CAC and is constantly waiting to catch up.

Lower CAC also gives you options. You can reinvest faster and test new channels. You can survive a bad month without panicking about covering your ongoing marketing spend. High CAC puts you on a treadmill where you have to keep selling just to stay in place.

CAC and lifetime value are inseparable

CAC on its own doesn’t tell the full story. It only becomes meaningful when you look at it next to lifetime value, or LTV.

LTV is how much profit you make from a client over the entire time they work with you.

A healthy rule of thumb for most service businesses is that LTV should be at least 3x CAC. If it costs you $500 to acquire a client, you want to make at least $1,500 in gross profit from them over time. Key word — profit, not revenue.

If your LTV is close to your CAC, your business is fragile. Any increase in ad costs, any drop in retention, any delay in payment, and the whole thing becomes unprofitable.

Using your CAC to make decisions

An easy test is to pull your CAC and your LTV and compare the two. If you are under a 3:1 ratio, start looking at what changes you need to make in the short term to your CAC, and in the medium term to your LTV, to rightsize this.

In the short term, you can reduce your CAC by reducing your marketing spend. Map out what your marketing spend would need to be per month to get to your 3:1 CAC:LTV target, and make those cuts immediately.

Once those short-term cuts are made, you can look at what to do to increase your LTV, which can make a longer-term difference in your CAC:LTV. Things that can increase LTV are increasing pricing or decreasing COGS, improving retention or improving your conversion rate. These things take time and experimentation, but it is usually worth the investment to work with a professional on these things to bolster your CAC:LTV math over time.

Ultimately, CAC tells you whether your business model actually works sustainably. It shows you the real cost of growth and whether the path you’re on pays off (literally).

If you don’t know your CAC today, that’s okay — but it’s not something to put off forever. The sooner you understand it, the sooner you can start making decisions that actually support the business you’re trying to build.