Customer Acquisition Cost (CAC)vsCAC Payback Period

CAC is the total cost of convincing a potential customer to buy your product. This includes all marketing spend, sales team salaries, tools, and overhead directly tied to acquiring new customers. The formula: CAC = Total Sales & Marketing Spend ÷ New Customers Acquired. A company spending $50K/month on marketing and sales and acquiring 100 customers has a $500 CAC. CAC varies dramatically by channel — paid ads might be $300 CAC while organic content is $30. VCs obsess over CAC because it determines unit economics: if CAC exceeds LTV, every customer you acquire destroys value.

The CAC Payback Period is how many months it takes for a customer to generate enough gross profit to cover the cost of acquiring them. It measures how quickly your business recoups its marketing investment. Formula: CAC ÷ (ARPU × Gross Margin). If your CAC is $600, ARPU is $100/month, and gross margin is 80%, payback = $600 ÷ ($100 × 0.80) = 7.5 months. VCs care about this as much as LTV:CAC because it determines your cash efficiency — a business with 3-month payback can reinvest acquisition dollars 4x per year, while a 12-month payback business can only reinvest once.

The most dangerous mistake is calculating 'blended CAC' by averaging all channels together. This hides the fact that your Google Ads channel might have a $200 CAC while organic has a $5 CAC. Blended CAC at $100 looks fine — but if you scale by doubling ad spend, CAC doesn't stay at $100; it approaches $200 because you're scaling the expensive channel. Always track CAC per channel. The second trap: excluding sales salaries from CAC. If you have 4 sales reps at $10K/month each and they close 40 deals/month, that's $1,000 in 'hidden' CAC per customer on top of marketing spend.

Bootstrapped founders with a payback period longer than 12 months will run out of cash before their customers become profitable. This is the #1 reason capital-efficient SaaS companies die — they acquire customers they can't afford to wait on. The second trap: ignoring that payback period should be calculated on CASH economics, not accrual. If you pay for ads today but customers pay monthly, your cash payback is always longer than your accounting payback.

Calculate CAC by channel: Paid CAC, Organic CAC, Referral CAC, Outbound CAC. For each: total spend on that channel ÷ customers from that channel. Kill channels where CAC > LTV/3 (not LTV/1 — you need margin for overhead). Track CAC trend monthly — increasing CAC often means market saturation or competitive pressure and requires immediate investigation.

Calculate: Payback Period = CAC ÷ (ARPU × Gross Margin). Target: under 12 months for bootstrapped, under 18 months for VC-backed. If payback exceeds these thresholds, either reduce CAC (cheaper channels), increase ARPU (pricing), or improve gross margin (lower costs). Also model payback by cohort — if it's increasing over time, you're acquiring worse-quality customers each month.