CAC (Customer Acquisition Cost)

What it is

Customer Acquisition Cost (CAC) is what it costs you, fully loaded, to convert one new paying customer. Add up every dollar spent on getting them in over a window (ad spend, sales-rep salaries, tooling, content, agency fees), then divide by the number of new customers in that window.

CAC = total sales and marketing spend ÷ new customers acquired

The window is usually one quarter for B2B SaaS, one month for fast-moving consumer products. Pick the window that matches the length of your sales cycle.

What “fully loaded” means

The number most founders quote is half the real CAC. Honest CAC includes:

Often counted	Often forgotten
Paid ads	SDR / AE salaries + commissions
Affiliate payouts	Content marketing salaries
Trade show booths	The marketing tools (HubSpot, ad platforms, attribution)
Influencer sponsorships	Free-trial infrastructure and support

If you only count ad spend, CAC looks 3-5× lower than it is. The ratio test below then says “we’re crushing it” when the business is actually upside-down.

The LTV/CAC test

CAC matters only against LTV. The ratio is the metric.

• LTV ÷ CAC < 1: every customer loses you money. Stop acquiring more until something changes.
• LTV ÷ CAC = 1 to 3: fragile. You survive only if retention stays high and acquisition costs don’t climb.
• LTV ÷ CAC ≥ 3: healthy. The unit economics scale.

David Skok’s SaaS Metrics 2.0 is the reference everyone uses. The 3× threshold is rough; some categories (high-margin B2B SaaS) tolerate 4×, others (consumer subscription with strong network effects) get away with 2×.

Worked example

A B2B SaaS team spends $20K on ads, $40K on one SDR’s quarterly compensation, and $5K on tooling and content in Q1. They close 50 new customers in the quarter.

• Total cost: $20K + $40K + $5K = $65,000
• Customers acquired: 50
• CAC = $65,000 ÷ 50 = $1,300

If LTV on those customers is $5,000, the ratio is 3.8×. Healthy. If LTV is $2,000, the ratio is 1.5×. Fragile, fix retention or pricing before pouring more into ads.

Common mistakes

1. Counting ad spend only. The biggest, most common mistake. CAC must include the people who run the campaigns and close the leads, not just the media buy.

2. Mismatched window. Spending Q1 dollars and dividing by Q4 customers (who were nurtured for nine months) tells you nothing useful. Match the window to the sales cycle.

3. Mixing channels. Paid CAC and organic CAC behave differently. Track them separately so you know which channel actually scales.

4. Treating CAC as fixed. As you scale, the cheap audiences saturate. Year-1 CAC almost always understates year-3 CAC for the same product.

Further reading

• David Skok, SaaS Metrics 2.0. The original LTV/CAC framework.
• LTV glossary. The number CAC is judged against.
• CAC/LTV ratio calculator. Drop your numbers in and get the verdict.