"What\'s your CAC?" "What\'s LTV?" These are the two most-asked questions in B2B SaaS, e-commerce, and any subscription business. The ratio between them determines whether you have a viable business or a cash incinerator. Here's the practical guide to both, plus the famous 3:1 rule.

CAC: customer acquisition cost

How much you spend, on average, to acquire a single new customer.

Formula: total sales + marketing spend / new customers acquired (in same period).

Example: spent $100k on sales/marketing in Q1, got 200 new customers. CAC = $500.

What goes in the CAC numerator

  • Paid advertising (Google, Facebook, LinkedIn ads)
  • Sales team salaries and commissions
  • Marketing team salaries
  • Marketing tools (CRM, analytics, email platforms)
  • Content production (blog, video, podcasts)
  • Events and trade shows
  • SEO/content investments

Sometimes these are split into "paid CAC" (just ads) and "fully-loaded CAC" (everything). For investor decks, fully-loaded is what matters.

LTV: lifetime value

The total revenue (or gross profit) a customer generates over their entire lifecycle.

Formula: ARPU × gross margin × (1 / churn rate).

Or simpler: monthly profit per customer × average customer lifetime in months.

Example: $50/mo ARPU × 70% gross margin × (1 / 5% monthly churn) = $35 × 20 = $700.

The 3:1 LTV:CAC ratio

Industry consensus: LTV should be at least 3× CAC for a sustainable business.

  • 1:1 or below: losing money. Each customer costs more than they're worth.
  • 1.5:1 to 3:1: tight. Profitable but limited room for error.
  • 3:1 to 5:1: healthy. Industry-typical for good SaaS.
  • 5:1+: excellent. Should consider investing more in growth.

Why 3:1? Below 3, the cost of acquisition eats too much of the lifetime value. Companies often need 30%+ for operations, marketing, and profit on top of CAC.

Worked examples

Healthy SaaS: CAC $500, LTV $2,500. Ratio 5:1. Profitable; should invest more in growth.

Tight SaaS: CAC $400, LTV $800. Ratio 2:1. Profitable but margins are thin. Each customer barely justifies acquisition.

Unprofitable: CAC $1,000, LTV $700. Ratio 0.7:1. Each new customer loses money. Without dramatic improvement, business will fail.

How to lower CAC

1. Improve conversion rate. Better landing pages, clearer value props, A/B testing. A 2% conversion rate at $5 CPC = $250 CAC. Boosting to 3% = $167 CAC.

2. Lower CPC. Better targeting, ad creative, search query optimization.

3. Increase organic traffic. SEO, content, viral loops. Free traffic = lower CAC.

4. Improve sales efficiency. Better discovery process, faster sales cycle, fewer touchpoints to close.

5. Cut wasteful channels. Some ad spend is wasted. Cut bottom 30% of channels by performance.

6. Referral programs. Existing customers refer new ones at very low CAC.

How to raise LTV

1. Reduce churn. Better onboarding, customer success, product improvements. 1% lower monthly churn = 20% higher LTV.

2. Raise prices. If pricing is below value, raise it. ARPU up = LTV up.

3. Upsell existing customers. Premium tiers, additional users, add-ons. Customer pays more per month.

4. Cross-sell related products. If customer has product A, offer product B.

5. Increase gross margin. Lower cost per customer increases profit per customer.

The CAC payback period

Related metric: how long does it take for monthly revenue to pay back the CAC?

Payback months = CAC / monthly revenue per customer.

$500 CAC / $50 monthly revenue = 10 months.

Industry rules of thumb:

  • Under 6 months: excellent.
  • 6–12 months: healthy.
  • 12–18 months: sustainable but tight.
  • Over 18 months: dangerous. Cash flow risk.

Long payback periods mean you front-load expenses and recover slowly — easy to run out of cash.

Cohort analysis

Instead of one CAC and one LTV, look by cohort:

  • January cohort: CAC $400, LTV after 12 months $600. Trending poorly.
  • April cohort: CAC $350, LTV after 12 months $700. Improving.
  • July cohort: CAC $300, LTV after 12 months $750. Continued improvement.

Cohort analysis reveals trends. If recent cohorts have improving CAC and LTV, your business is getting better. If degrading, danger.

Channel-specific CAC

Different channels have different CAC. Track them separately:

  • Google Ads: $300 CAC, 2:1 LTV ratio.
  • Facebook Ads: $200 CAC, 3:1 LTV ratio.
  • LinkedIn: $1,200 CAC, 4:1 LTV ratio.
  • Organic SEO: $50 CAC, 8:1 LTV ratio.
  • Referrals: $100 CAC, 10:1 LTV ratio.

Allocate marketing budget toward higher-ratio channels. Cut lower-ratio ones.

The "growth phase" exception

Early-stage startups sometimes operate at LTV:CAC of 1:1 or worse to build market share. Goal: efficient growth.

This is rarely sustainable. Eventually you must hit 3:1 or fail. Investors fund the unprofitable phase if growth justifies it.

Cohort vs blended CAC

Blended CAC: total spend / total customers. Easy to calculate.

Channel-specific CAC: separate by channel. More work but more useful.

Marginal CAC: cost of acquiring the next customer. Often higher than average (you're targeting harder-to-reach prospects).

Calculate yours

Our CAC calculator and LTV calculator handle the math. Use both to compute your own ratio. Then track quarterly — improvements should be measurable.