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Cohort Payback Curve Calculator

Estimate when a cohort pays back CAC using a simple retention curve (two-stage churn) and optional expansion.

Payback is a cash reality check. Even if LTV is high, you can still fail if payback is too slow for your cash runway.

This calculator estimates cohort payback using a two-stage retention model (higher churn early, lower churn later) and optional expansion on surviving customers.

Prefer an explanation- Read the guide.

Cohort payback curves: how to model payback with early churn Cohort analysis playbook: retention curves, LTV forecasting, and payback Unit economics dashboard: LTV, CAC, payback, and what to improve Retention curves: how to read them and why they matter

CAC (per new customer)

ARPA (monthly)

Gross margin

Early monthly churn

Early phase months

Steady-state monthly churn

Monthly expansion (optional)

Expansion applied to surviving customers (set 0 to disable).

Months to model

Tip: you can type commas (e.g., 10,000).

Example

Using the default inputs, the result is:

10.9 months

CAC (per new customer): $6,000
ARPA (monthly): $800
Gross margin: 80%
Early monthly churn: 6%
Early phase months: 3
Steady-state monthly churn: 1%
Monthly expansion (optional): 0.5%
Months to model: 36

How to calculate

Enter ARPA and gross margin to compute monthly gross profit per active customer.
Enter CAC per new customer and your early vs steady-state churn assumptions.
Optionally add monthly expansion to model upgrades/seat growth.
Review the payback month and cumulative gross profit over the horizon.

Formula

Cumulative gross profit = sum (retained_customers_t x ARPA_t x gross margin); Payback occurs when cumulative gross profit >= CAC

Two-stage logo churn (early vs steady-state).
Expansion applies to surviving customers' revenue each month (simplified).
Gross margin is constant and used as a proxy for gross profit.

FAQ

Why model early churn separately-

Because early churn often dominates payback. Improving activation and onboarding can dramatically reduce payback even if steady-state churn is unchanged.

Should I use logo churn or revenue churn-

Payback is about cash from customers. If expansion and downgrades matter, model revenue retention curves (NRR/GRR). Logo churn is still useful for intuition but can miss dollar effects.