LTV/CAC: Unit Economics for Subscription Growth

For educational purposes only; not investment advice.

Direct answer

LTV/CAC compares estimated customer lifetime value with the cost to acquire that customer. It is often used for SaaS, subscription, marketplace, and consumer internet companies to judge whether growth spending is creating valuable customers or merely buying revenue.

A high ratio can be positive, but it is not automatically good. The ratio depends on retention, gross margin, pricing, sales efficiency, cohort quality, and company-specific definitions. Investors should read the disclosure behind the metric before comparing companies.

Mechanism

A simplified version is:

LTV/CAC = estimated customer lifetime value ÷ customer acquisition cost

One common simplified LTV formula is:

LTV ≈ annual gross profit per customer ÷ annual churn rate

CAC may be estimated as:

CAC = sales and marketing expense ÷ new customers acquired

These formulas are only starting points. Companies may define customers, churn, sales expense, partner commissions, onboarding, renewals, and expansion revenue differently. Some costs occur before revenue appears, while some customers generate revenue for many years.

LTV/CAC should therefore be read with CAC payback period, gross margin, net revenue retention, free cash flow, and dilution. Growth is stronger when a company can recover acquisition spend quickly, retain customers, expand account value, and convert revenue into cash.

Example

Suppose a software company spends $12 million on sales and marketing in a quarter and adds 3,000 customers.

CAC = $12m ÷ 3,000 = $4,000

If each customer produces $2,000 of annual revenue and gross margin is 75%, annual gross profit per customer is:

$2,000 × 75% = $1,500

If annual churn is 20%, simplified LTV is:

$1,500 ÷ 20% = $7,500

The simplified LTV/CAC ratio is:

$7,500 ÷ $4,000 = 1.875x

If churn improves to 10%, simplified LTV rises to $15,000 and the ratio becomes 3.75x. The same CAC looks much better because retention changed. If sales spending excludes important commissions or onboarding costs, the ratio may be overstated.

Risks

Metric definition risk: LTV/CAC is usually non-GAAP and not standardized.
Churn sensitivity: small retention changes can dramatically change estimated LTV.
Gross margin risk: revenue with low service or delivery margins produces weaker lifetime value.
Timing mismatch: acquisition spend may precede revenue by several periods.
Cohort mix risk: early adopters can be cheaper and stickier than later customers.
Expansion assumption risk: including upsell and price increases can make LTV optimistic.
Cash-flow risk: a good ratio can still hide long payback periods and heavy funding needs.

Common misconceptions

“A ratio above 3x is always excellent.” Rules of thumb ignore industry, margin, churn, payback time, and cost definitions.

“LTV is a reported asset.” It is an estimate, not a balance-sheet asset under standard reporting.

“High growth proves strong unit economics.” Growth may come from aggressive spending, discounts, or low-quality channels.

“CAC is only advertising.” For many companies it includes salespeople, commissions, software, partners, events, and onboarding costs, depending on the definition.

Sources

SEC: non-GAAP measure guidance and 10-K reading framework for checking company-defined metrics.
SSRN: research background on customer acquisition cost, retention, and customer lifetime value.
FASB: revenue recognition context for customer contracts and reported revenue.