CAC payback vs customer lifetime value: formulas and churn example
Compare constant-margin CAC payback with a finite lifetime-value model, see how churn changes recovery, and keep acquisition-cost definitions consistent.
Define acquisition cost for a specific cohort
Customer acquisition cost divides the acquisition spending you include by the new customers acquired under a consistent definition. Record the cohort dates, the spending categories and the customer qualification rule. A media-only figure differs from a fully scoped figure including acquisition labor and other expenses. Align spending and customer timing thoughtfully when the sales process spans several periods. Do not compare an all-company marketing numerator with customers from one small campaign. Keep the cohort definition beside the result so a later payback or lifetime-value comparison does not quietly change the underlying population.
Calculate constant-margin payback with a clear example
Suppose CAC is 600, monthly customer revenue is 120 and gross margin is 75%. Monthly gross profit is 90. The customer acquisition payback calculator returns 600 ÷ 90, or about 6.6667 months. If the modeled amount arrives at each month end, the first fully recovered month is seven. This calculation assumes that the customer stays active and that monthly revenue and margin remain constant. It answers how long an uninterrupted stream would need to recover the acquisition cost. It does not establish that every acquired customer will remain long enough.
Add churn and a finite observation window
Enter monthly revenue 120, margin 75%, monthly churn 12%, CAC 600 and a twelve-month finite horizon in the lifetime value calculator. It returns expected modeled contribution of about 588.25, an LTV:CAC ratio of 0.9804:1 and value after acquisition cost of negative 11.75. The model begins with every customer active in month one, then applies the same chance of departure at each month end. Expected contributions decline with the surviving share. This result can coexist with a 6.6667-month constant-margin payback: the models make different assumptions about continued activity.
| Model | Assumptions | Result |
|---|---|---|
| Constant-margin payback | CAC 600; monthly revenue 120; margin 75% | 6.67 months; first whole recovery month 7 |
| Finite lifetime contribution | Same revenue/margin; churn 12%; horizon 12 months | About 588.25 before CAC |
| Finite contribution less CAC | 588.25 − 600 | About −11.75 |
Churn applies after each active month in the finite model. Constant-margin payback does not include churn.
Read the churn result as an expectation
The finite model sums monthly contribution multiplied by the probability of remaining active for that month. It does not predict a fractional customer’s actual payment schedule. Some customers may leave before recovery; others may remain much longer than twelve months. A cohort’s aggregate result depends on its observed retention and revenue pattern. Keep those observations separate from the simplified constant-churn model. If onboarding contracts, annual renewals or seasonal behavior produce uneven departures, review the actual cohort curve rather than assuming the same departure probability fits every month.
Name the margin basis before comparing ratios
Gross margin deducts the costs included in cost of revenue; a contribution-margin scope may include additional variable costs you want to recover before acquisition spending. A payback figure using 75% gross margin is not directly comparable with an LTV calculation using a lower contribution rate. Decide which costs belong in the question, record the basis, and use matching inputs in both calculators. Fixed overhead and financing timing still need separate review. Calling the output lifetime net profit would overstate what the simplified model has established if those expenses are absent.
Keep finite and long-run value separate
Under positive constant churn, the theoretical long-run geometric model divides monthly contribution by the churn rate. With contribution 90 and churn 12%, that is 750 before acquisition cost. The twelve-month value is lower because it excludes contributions beyond the chosen horizon. Neither result guarantees those future receipts. Zero churn with positive contribution makes the infinite-horizon arithmetic unbounded, which exposes the assumption rather than proving endless value. Use a finite period appropriate to the decision and explain why that period matters, especially when current cash must fund acquisition well before future contributions arrive.
Include acquisition time in a service-business review
For a freelancer, proposals, unpaid discovery and sales calls can represent an acquisition investment even when advertising spend is small. Keep a record of that time and its chosen costing basis instead of reporting zero CAC simply because no ad invoice exists. The freelance minimum hourly rate calculator estimates a billing floor from income goals, expenses and billable capacity; it is not a CAC calculator. Its capacity analysis can help reveal how acquisition work reduces billable time. Avoid counting the same time both as a separate acquisition expense and again in an inconsistent overhead allocation.
Use both models to choose the next investigation
Save the constant-margin payback calculation and the finite churn-adjusted value for the same cohort and margin scope. Compare them with observed customer receipts, servicing costs and retention at successive ages. If payback looks short but finite value does not recover CAC, investigate early departures and the acquisition mix. If expected value is high but cash recovery is delayed, review the financing and collection schedule. Do not replace that investigation with a universal ratio benchmark. The useful next step is the one that explains the gap between the saved assumptions and your own cohort evidence.