A campaign with a high ROAS can still leave the business short of cash. A channel with a low CAC does not necessarily bring good customers. CAC, LTV and ROAS are only useful when calculated consistently and read next to margin, cash flow and payback period.
You do not need a complex financial model to start. What matters more is defining clearly which costs are included, which revenue has actually been recognised, and how differently each customer group behaves.
CAC: the cost of acquiring one customer
CAC is total sales and marketing spend in a period divided by the number of new customers it produced. Beyond the ad budget, include people, tools, content production, commissions and agency fees where they serve customer acquisition.
Note: Do not compare a channel CAC that only counts ad spend with a company-wide CAC that includes salaries and tools; the two numbers use different definitions.
LTV: customer value across the relationship
LTV should reflect contribution profit, not just revenue. For repeat-purchase models you can start with average order value multiplied by purchase frequency and retention period, then multiply by the margin. When data is thin, use conservative estimates and update them per customer group.
ROAS: revenue per unit of ad spend
ROAS is the revenue attributed to advertising divided by the advertising cost. It is easy to read but does not deduct cost of goods, payment fees, operations and refunds. The break-even ROAS for a business with a 30% gross margin is very far from one with an 80% margin.
Read the three together
- ROAS shows how efficiently the ad budget generates short-term revenue.
- CAC shows the total cost required to win a new customer.
- LTV shows whether you can recover CAC and profit afterwards.
- Payback period shows how long the business must fund its own growth.
- Cash flow shows whether the current pace of expansion is affordable.
A reporting process you can audit
- 01
Lock the definitions
Write down the data source, the time window and which cost types belong in each metric.
- 02
Break it down
View by channel, campaign, product and customer group rather than one average number.
- 03
Reconcile
Compare the revenue in the ad tool against orders, refunds and money actually received.
- 04
Decide
Raise the budget when profit and payback allow it, not just because the dashboard is green.
