Choose a customer unit and acquisition cohort
Define whether one unit is a logo, workspace, paid seat or contract. The unit used for CAC must match the revenue and retention unit used for LTV. Then freeze an acquisition cohort by channel and period. Blending self-serve signups with enterprise contracts produces an average that describes neither motion because sales cost, onboarding time, expansion and churn differ.
CAC should include the costs required to acquire the cohort: media, sales and marketing payroll, commissions, agencies, tools and attributable partner fees. Record the cost window and treatment of brand activity. A narrower paid-media CPA can remain useful, but it should not be labeled as fully loaded CAC.
Build gross contribution before LTV
Start with net recurring revenue after discounts and credits. Subtract infrastructure, third-party services, payment processing, support and direct delivery payroll under a documented cost-of-revenue policy. The result is gross contribution available to recover acquisition and operating costs. Revenue LTV overstates the acquisition budget whenever gross margin is below 100%.
Segment delivery cost when usage varies. An average infrastructure allocation may make light customers appear worse and heavy customers appear better. Marginal cost helps price an additional unit, while fully allocated cost helps evaluate segment profitability. Both views should be named rather than mixed.
Treat LTV as a sensitivity model
A simple LTV formula divides monthly gross profit by monthly churn. That assumes a stable churn rate, constant gross margin and no discounting. These assumptions are strongest for mature, homogeneous cohorts and weakest for early products, annual contracts and businesses where retention changes sharply with tenure.
Use cohort revenue and gross-profit curves when sufficient history exists. Limit the forecast horizon, show realized contribution separately from projected tail value and run higher-churn and lower-margin cases. The range is more useful for a budget decision than a precise but fragile point estimate.
Use payback to expose cash timing
CAC payback measures the months of gross contribution required to recover acquisition cost. Model onboarding and ramp periods rather than assuming full contribution from month one. Billing terms also matter: an annual prepayment can support cash even when accounting contribution is recognized over time, while monthly billing may leave the company financing sales expense.
Compare payback with runway, retention and growth capacity. A high LTV:CAC ratio does not solve a cash gap if acquisition is paid today and recovered years later. Conversely, an efficient short payback may justify reinvestment even before long-term LTV is fully observed.
Create a cohort review loop
At a fixed cadence, compare forecast and realized new customers, CAC, activation, gross margin, retention and cumulative contribution for each important acquisition cohort. Investigate definition changes before performance changes. Update budgets only after the relevant cohort has enough observation time for the decision being made.
- Keep paid-media CPA and fully loaded CAC as separate measures.
- Use gross contribution, not revenue, for payback and LTV.
- Show modeled, realized and downside values separately.