Move from total cost to the chosen unit
Consider a hypothetical model. Reconcile revenue, direct cost, and sales expense to the financial statements before allocating them by customer, contract, or transaction. An unexplained allocation should not produce a falsely precise unit result.
Define what acquisition cost includes
Sales salaries, commissions, marketing, channel share, and pre-launch support all change acquisition cost. The model should state the employee population, attribution period, and treatment of teams serving both new and renewing customers.
Match contribution margin to operating activity
Subscription software, payment transactions, and people-led services have different direct costs. Cloud resources, third-party data, payment fees, and support do not disappear merely because accounting places them below gross profit.
- Identify costs that vary with customers or usage.
- Review fixed commitments and minimum purchases.
- Separate one-time implementation from recurring service.
Treat payback as a model output
Payback depends on margin, churn, and cash collection. If any input comes from an immature cohort or an untested allocation, show sensitivity rather than a single authoritative number. The model compares cases; source evidence carries the conclusion.