averagecac.com

The unit-economic ratio everyone quotes

The LTV:CAC Ratio

Lifetime value divided by customer acquisition cost. Above 3:1 is the canonical SaaS rule of thumb for a healthy unit economic. Below 1:1 means you lose money on every customer. The rule is a starting point, not a law.

The formula

LTV:CAC = (Monthly ARPU × Gross Margin × Avg Lifetime in Months) ÷ CAC

LTV (the numerator inside the parens) is the total gross profit one customer is expected to generate over their lifetime. Average lifetime in months is typically computed as 1 ÷ monthly churn rate. CAC is the denominator outside the parens, computed per our CAC formula page.

The 3:1 rule and where it came from

The 3:1 LTV:CAC heuristic was popularised by David Skok's SaaS Metrics 2.0 series (Matrix Partners, originally 2013, updated since). The argument: at 3:1, you generate $3 of gross profit over a customer's lifetime for every $1 spent acquiring them, leaving enough margin to cover R&D, G&A, and a return on capital.

The 3:1 rule isn't a law of physics. It assumes your CAC and LTV are both measured honestly and your gross margin is in the 70-85% range typical of pure software. Businesses with capital-intensive infrastructure (some marketplaces, hardware + software), heavy services components, or unusually high churn need higher ratios to look healthy.

Why the LTV side is fragile

LTV = ARPU × Gross Margin × Average Lifetime. Two of those three inputs (gross margin, ARPU) are observable. The third (average lifetime) is computed as 1 ÷ monthly churn, which compounds assumption errors:

When the LTV input is shaky, the payback period metric is more defensible: it depends only on CAC and current gross profit per customer, no churn assumption required.

Common questions

LTV:CAC questions

What is a good LTV:CAC ratio?
Above 3:1 is the canonical SaaS rule of thumb. Between 1:1 and 3:1 means unit-economic positive but unlikely to fund growth comfortably. Below 1:1 means losing money on every customer. Above 5:1 sometimes signals under-investment in growth; the company could profitably spend more on acquisition.
What is the source of the 3:1 LTV:CAC rule of thumb?
The 3:1 rule was popularised by David Skok (Matrix Partners) in his SaaS Metrics 2.0 series on forEntrepreneurs.com, first published in the early 2010s and updated since. The reasoning: at 3:1 you generate $3 of gross profit over a customer's lifetime for every $1 spent acquiring them, leaving enough margin to cover R&D, G&A, and a return on capital. It is a guideline for mature, steady-state software businesses, not a law of physics, and assumes gross margins in the 70-85% range and honestly measured CAC and LTV.
How do I compute LTV:CAC?
LTV:CAC = (Monthly ARPU × Gross Margin × Average Lifetime in Months) ÷ CAC. Average lifetime in months = 1 ÷ monthly churn rate. Use our calculator at /calculator/ to compute both numerator and denominator with your inputs.
Why is LTV:CAC unreliable for early-stage companies?
LTV requires an assumption about average customer lifetime, which is 1 ÷ monthly churn. Early-stage companies don't have enough cohort data to estimate monthly churn reliably, so the lifetime denominator is a guess. The error compounds: a 0.5% miss on churn produces a 33% miss on LTV.
Should I use LTV:CAC or payback period?
Payback for external reporting and when churn data is uncertain. LTV:CAC for internal modelling when your churn assumption is grounded in cohort data. The two metrics are complementary: payback tells you when each customer becomes economic; LTV:CAC tells you how economic they ultimately become.