Unit Economics

CAC Payback: CAC Payback Period

The number of months to recover the cost of acquiring a customer from gross-margin contribution.

Definition

CAC Payback Period is the number of months it takes to recover the cost of acquiring a customer from the gross-margin contribution of that customer. Below 12 months is healthy for SaaS; below 18 months is acceptable; above 24 months is a structural concern.

Formula

CAC Payback = CAC ÷ (Monthly ARPA × Gross Margin)

CAC Payback (months) = CAC / (Monthly ARPA × Gross Margin)

Worked example

CAC of £6,000, ARPA of £500/month, gross margin of 80%. Monthly contribution is £400. Payback = £6,000 / £400 = 15 months.

Why it matters

Payback period determines cash flow. If payback is 18 months, you need 18 months of working capital per cohort before seeing returns. Shorter payback compounds: faster cash recycling means faster reinvestment into growth.

Common mistakes

  • Using revenue rather than gross-margin contribution in the denominator (understates payback)
  • Excluding fully-loaded sales salaries from CAC
  • Assuming retention to 100% of the payback window in high-churn segments

Related terms

CACLTVMagic NumberGross Margin

Read more in The Guide

Chapter: Unit Economics →

Sources & further reading

  • — Drawn from Evara's working definitions used on retained search and revenue advisory engagements (2024–2026).
  • — Reconciled against industry conventions in SaaStr, OpenView SaaS Benchmarks and Bessemer State of the Cloud.
  • — Reviewed by Rich Evans, Strategic Advisor at Evara and former operator/founder.

Hiring a leader who needs to own this metric? See our salary benchmarks →

Talk to Evara.

Sales recruitment, GTM recruitment and revenue advisory for SMEs UK-wide. We reply within one working day.

Email Rachel Lunn