ARR, CAC, LTV and churn: the four pillars of SaaS growth
Growth in a subscription business cannot be reduced to one number. ARR sizes annualised recurring revenue, CAC prices the full cost of acquiring a customer, LTV values the total revenue that customer contributes over the relationship, and churn measures how quickly existing customers leave. Read together, they reveal whether growth is genuinely sustainable.
How the metrics influence each other
When churn rises, average customer lifetime shortens, which directly reduces LTV. A lower LTV against an unchanged CAC breaks your unit economics. Reducing churn is therefore often a faster profitability lever than acquiring new customers. Likewise a price increase lifts both ARR and LTV but can trigger churn, so changes should be measured one at a time.
Why LTV:CAC is the most important ratio
LTV:CAC tells you how many times over you recover the money spent to win a customer. A 3:1 ratio is the accepted healthy benchmark. Approaching 1:1 means you lose money as you scale; above 5:1 usually means you are underinvesting in growth and could spend more on acquisition. CAC payback period is typically expected to stay under 12 months.
A concrete scenario: the order a SaaS founder should follow
First, use the ARR Calculator to annualise current subscription revenue and establish scale. Second, use the CAC Calculator to divide last quarter's full sales and marketing spend by new customers won. Third, use the Churn Rate Calculator to find your monthly loss rate, which yields average customer lifetime. Finally, use the LTV Calculator and compare the result against CAC. If the ratio sits below 3:1, address churn first, pricing second and acquisition channels last.
Common reporting mistakes
The most frequent error is mixing periods — comparing a monthly CAC against an annual LTV distorts everything. The second is counting only ad spend in CAC while excluding sales salaries and tooling. The third is treating revenue churn and customer churn as the same thing; losing one large account barely moves customer count but can wreck revenue.