The metrics that matter: CAC, LTV and payback

In Accelerate, the question is no longer whether the product works but how much growth the business can afford and how quickly it can buy it. Three numbers govern that: what a customer costs to acquire, what a customer is worth, and how long the cash takes to come back.

Customer acquisition cost

CAC is total sales and marketing cost in a period divided by the number of new customers acquired in that period. The word doing the work is total: salaries, commission, tooling, agency fees, content and events, not just advertising spend. Excluding sales salaries is the most common way CAC is understated, and it flatters everything downstream.

• Include fully loaded sales and marketing salaries and commission.
• Exclude customer success costs that serve existing customers, and account for them in gross margin instead.
• Calculate by channel, because a blended CAC hides the channel that is quietly unprofitable.
• Allow for the lag between spend and closed business in longer sales cycles.

Lifetime value

For a subscription business, LTV is average revenue per account multiplied by gross margin, divided by monthly churn rate. Using revenue rather than gross profit is the second most common distortion — a business with a 60% margin and one with a 90% margin do not have the same LTV on identical revenue.

A commonly cited benchmark is an LTV:CAC ratio of at least 3, but the ratio on its own is a weak instrument. A very high ratio often means the business is under-investing in acquisition rather than performing well. Read it alongside payback.

Payback is the constraint that actually binds

Payback period is CAC divided by monthly gross profit per customer — how long before an acquired customer has repaid the cost of acquiring them. It matters more than LTV:CAC for one practical reason: it determines how many customers you can acquire per year with a given amount of cash. A twenty-four-month payback means capital is tied up for two years per customer, which caps growth regardless of how attractive the lifetime value looks.

Instrument by cohort and by channel

Blended, company-wide numbers describe the average of a set of very different behaviours and are close to useless for decisions. Cohorts show whether the business is improving over time. Channel breakdowns show where the next pound should go. Segment breakdowns show which customers you should be selling to and which you should politely stop pursuing.

This is a measurement architecture decision as much as an analytics one, and it is far cheaper to build in during Launch than to retrofit later — a point we develop in structuring a venture for scale.

Used well, these three numbers convert growth from an ambition into a plan with a rate attached. That is precisely the conversation investors expect at this stage, as covered in venture builder vs venture capital.

Reading the three numbers together

CAC, LTV and payback are frequently reported side by side and interpreted separately, which is how a business with a healthy-looking ratio runs out of cash. The ratio describes eventual profitability; payback describes how long the money is gone for. A venture with a strong LTV:CAC ratio and a twenty-four-month payback is a business that needs a great deal of funding to grow at any speed, and that is a strategic fact worth knowing before the growth plan is signed off rather than after.

Answering all four honestly is usually the difference between scaling a working engine and buying revenue at a loss. It is also the conversation that makes a Series A discussion straightforward, because the company can state its growth rate as a function of capital rather than as a projection.

None of this requires sophisticated analytics tooling in the early years. It requires that the definitions are agreed once, applied consistently, and reported to the board in the same form every month. Businesses that change how they calculate CAC each quarter cannot tell whether they are improving, and neither can anyone else looking at them.