SaaS CAC payback calculator

Compare a simple gross-margin payback ratio with a fixed monthly churn scenario for the same new-customer cohort.

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Use consistent customer, period and currency definitions.

COHORT COMPARISON

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Estimated payback

Scenario per original customer, not a guarantee. Churn is applied after each full month; no expansion, discounting, upfront cash timing, taxes or changing margin is modeled.

METHOD & INTERPRETATION

How SaaS CAC payback works

Divide acquisition cost per new customer by monthly recurring revenue per active customer multiplied by the recurring gross margin. The result is a simple fractional-month ratio; it assumes the same contribution every month and ignores customers leaving during payback.

What changes in the churn scenario?

The scenario starts with one average original customer. It assumes a constant share of remaining customers leaves at the end of each month. Expected gross contribution in month one is revenue × gross margin; in month two it is that amount × (1 − churn), and so on. We add complete months until the cumulative expected contribution per original customer reaches CAC or the selected horizon ends. The result is a cohort expectation, not a prediction of when any individual customer pays back.

For example, with $1,000 CAC, $100 monthly recurring revenue, 80% gross margin and 2% monthly churn, the simple ratio is 12.5 months. Under the stated churn timing, the cumulative scenario reaches $1,000 during completed month 15. A shorter observation horizon may show that payback has not yet been reached; that alone does not mean it will never happen.

Use comparable definitions

Match the acquisition costs and new-customer count to the same cohort and period. Define which delivery costs are included in gross margin and avoid counting acquisition spend twice. Different company reporting methods may use revenue, gross profit, bookings or different time periods, so compare like with like.

What the model leaves out

It assumes constant recurring revenue, margin and churn, with the first full month earning revenue before churn. It excludes expansion, downgrades, refunds, changes in costs, taxes, financing and the timing of annual upfront payments. It is a planning illustration, not accounting or investment advice. Compare the model with actual cohort cash flows before making decisions.

Benchmarkit’s SaaS metrics definitions provide context for a gross-margin-adjusted CAC payback ratio. Definitions and reporting periods vary by organization.