LTV:CAC Ratio
The ratio of customer lifetime value to customer acquisition cost — the fundamental unit-economics test of whether a business model works.
What Is the LTV:CAC Ratio?
LTV:CAC is the ratio of customer lifetime value to customer acquisition cost. It measures whether the money you spend to acquire customers returns substantially more than it cost. The common rule of thumb: below 1:1 you lose money; 1:1 to 3:1 you're undercutting profit; 3:1 is healthy; above 5:1 you may be underinvesting in growth.
Also Known As
- Finance teams: unit economics ratio, LTV:CAC multiple
- Growth teams: payback efficiency
- Investor view: capital efficiency ratio
- Board reports: lifetime-value ratio
How It Works
A SaaS customer pays $100/mo with 80% gross margin and 3% monthly churn. LTV = ($100 × 0.80) / 0.03 = $2,667. The company spends $800 in blended S&M to acquire that customer. LTV:CAC = $2,667 / $800 = 3.3. That's healthy. Now imagine CAC rises to $1,500 as paid channels saturate. Ratio drops to 1.8 — below the 3:1 threshold. The company should pause CAC-heavy channels and find more efficient acquisition before scaling further.
Best Practices
- Do use gross-margin-adjusted LTV, not raw revenue × lifetime. Revenue that doesn't contribute margin isn't real LTV.
- Do compute LTV and CAC by channel. Blended ratios can hide a channel that's bleeding money.
- Do use cohort-based LTV, not modeled LTV, when possible. Real data beats formulas.
- Don't chase a 10:1 ratio. It usually means you're underspending on growth and competitors are passing you.
- Don't inflate LTV with expansion you can't actually predict. Be conservative.
Common Mistakes
- Using revenue LTV instead of gross profit LTV. An 80% margin business and a 20% margin business with the same LTV:CAC are not comparable.
- Ignoring payback period. A healthy LTV:CAC with a 36-month payback still strains cash flow.
Industry Context
SaaS: target 3:1, payback 12-18 months. Ecommerce: target 3:1+ on first-order basis, much higher with repeat purchases. Lead gen / agency: often 5:1+ because no recurring revenue justifies long payback. Marketplaces: highly dependent on take rate and transaction frequency.
The Behavioral Science Connection
LTV:CAC is the business equivalent of expected value calculation — it forces teams to reason about probability-weighted future value rather than relying on short-term optimism. It counters sunk cost fallacy in channel decisions: the fact that you've spent $2M on a channel doesn't matter if the current ratio is 0.8.
Key Takeaway
LTV:CAC is the most honest test of whether your business model works. A company with great top-line growth and bad LTV:CAC is burning money to buy customers that don't return enough. The ratio is the truth.