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Customer Acquisition Cost, Customer Lifetime Value

Customer Acquisition Cost Vs Lifetime
Value.

Updated

If you only get one ratio right in a subscription business, it is LTV:CAC. Everything else flows from it. Pricing decisions, marketing budgets, growth investments, hiring plans — all of them implicitly bet on this ratio. Get it consistently above 3:1 and you can scale aggressively. Stuck below, and every new customer is a slow loss.

The two numbers, clean definitions

  • CAC (Customer Acquisition Cost) — Total sales and marketing spend divided by new customers acquired in the same period. Includes paid ads, organic content costs, agency fees, and acquisition-attributable headcount.
  • LTV (Customer Lifetime Value) — Gross profit expected from a customer across their entire subscription lifetime. Common formula: (average revenue per customer per period × gross margin) ÷ monthly churn rate.

Why the 3:1 benchmark

The 3:1 rule comes from SaaS economics but applies cleanly to subscription ecommerce too. The logic: 1x covers acquisition, 1x covers ongoing operations and overhead, 1x is profit or growth reinvestment. Below 3:1, the unit economics get thin; above 5:1, you may be leaving growth on the table by under-spending on acquisition.

Worked example for a Shopify subscription store

Imagine a coffee subscription store:

  • Average revenue per subscriber: $30/month
  • Gross margin: 50% ($15/month)
  • Monthly churn: 6%
  • LTV: $15 ÷ 0.06 = $250
  • CAC (paid ads, content, attribution): $80
  • LTV:CAC ratio: 3.1 — healthy

Now imagine churn rises to 10%. LTV drops to $150. Ratio collapses to 1.9 — every acquired customer is now near breakeven, and growth becomes unprofitable. This is why churn is the single biggest lever in subscription unit economics.

Common mistakes

  1. Using revenue instead of gross profit in LTV. Overstates LTV by the cost-of-goods-sold percentage. For a 50% margin product, LTV is 2x too high.
  2. Underestimating CAC. Ignoring agency fees, organic content costs, or attribution leakage. True CAC is often 30–50% higher than reported.
  3. Treating LTV as forecast rather than estimate. LTV based on current churn assumes that churn stays put. If you have only had subscribers for 3 months, the LTV is a guess, not a number.

For the underlying metrics, see customer acquisition cost and customer lifetime value.

Frequently Asked Questions

What is a good LTV to CAC ratio?

3:1 is the standard benchmark — meaning a customer's lifetime gross profit is three times what you spent to acquire them. Above 3:1 is healthy; below 3:1 signals that unit economics are thin and growth may be unprofitable; well above 5:1 may indicate you are under-investing in acquisition.

How do I calculate LTV for a Shopify subscription store?

The simplest formula: (average revenue per subscriber per month × gross margin %) ÷ monthly churn rate. So a $30/month subscriber with 50% gross margin and 6% monthly churn has an LTV of ($30 × 0.50) ÷ 0.06 = $250. Use gross profit, not revenue — using revenue inflates LTV significantly.

Why is LTV:CAC the most important subscription metric?

Because it tells you whether each new customer is profitable over their lifetime. If the ratio is healthy, you can scale acquisition spend confidently — every dollar in produces multiple dollars out. If the ratio is broken, no amount of growth fixes the business; you are just losing money faster.

What is the fastest way to improve LTV:CAC?

Almost always: reduce churn. LTV is inversely proportional to churn, so cutting monthly churn from 8% to 6% increases LTV by a third. That is usually a bigger lever than reducing CAC, which is constrained by competitive bidding and channel saturation. Fix retention first.

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