This Series A Payback Estimator calculates how many months of gross profit are needed to recover customer acquisition cost. It also estimates cumulative cash contribution after a chosen horizon and the CAC remaining to be recovered.
Payback is especially useful when growth spending competes with runway. Enter CAC, monthly revenue per customer, gross margin, and a horizon. The model assumes flat monthly revenue and margin, so it should be adjusted for ramp periods, onboarding costs, or variable expansion when those are material.
1. Enter CAC
Use the fully loaded acquisition cost for the customer segment.
2. Enter monthly revenue
Use average recurring revenue per acquired customer.
3. Set gross margin
Exclude direct delivery costs by entering the expected gross margin.
4. Choose a horizon
Enter the number of months for the contribution check.
5. Review recovery timing
Compare payback months with cash runway and customer retention expectations.
The model assumes immediate, constant monthly revenue and gross margin. It excludes revenue ramp, churn before payback, discounting, and one-time onboarding or implementation costs.
Payback period is the number of months of gross profit required to recover acquisition cost.
A customer must remain active through the payback period for the modeled recovery to occur.
Given
Calculation
Monthly gross profit = $500 × 0.80 = $400. Payback = $3,000 / $400 = 7.5 months. Twelve-month contribution = $400 × 12 - $3,000 = $1,800.
Result
Estimated payback period = 7.5 months.
At 12 months, the modeled customer has recovered CAC and generated $1,800 of gross-profit contribution after acquisition cost.
Include onboarding cost if it is part of acquiring and activating the customer under your internal unit-economics policy.
This flat-revenue model may understate payback during a slow ramp or overstate it when revenue declines. Use a monthly cohort schedule for precision.
If customers churn before the calculated payback month, the expected acquisition cost may not be fully recovered.
Gross profit reflects the revenue left after direct service costs and is therefore available to repay CAC.
Payback focuses on recovery speed. LTV:CAC compares total expected customer value with acquisition cost.