Paid AcquisitionvsCustomer Acquisition Cost (CAC)

Paid acquisition is spending money on ads to acquire customers — Google Ads, Meta Ads, LinkedIn, TikTok, etc. The core equation is simple: if you spend $100 on ads and get 2 customers, your paid CAC is $50. The channel is scalable but has diminishing returns — the first $10K/month is often 3-5x more efficient than the next $100K/month because you exhaust the best-fit audiences first.

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 fatal trap is scaling paid spend before knowing your unit economics. If your LTV is $200 and your paid CAC is $80 at $5K/month spend, you assume it'll stay at $80 when you 10x to $50K/month. In reality, paid CAC typically increases 30-60% as you scale because you move from high-intent searchers to broader, less-qualified audiences. Many startups burn through their runway scaling a channel that was only profitable at small budgets.

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.

Calculate your Paid CAC Payback Period: Paid CAC ÷ (Monthly ARPU × Gross Margin). If payback is under 6 months for B2B SaaS or under 3 months for B2C, you can scale confidently. Track ROAS (Return on Ad Spend) weekly: Revenue from paid customers ÷ Ad spend. Target a minimum 3:1 ROAS for sustainable growth.

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.