CAC payback is how many months a new customer must stay before their cumulative gross profit repays the upfront S&M cost to acquire them. Top-quartile B2B SaaS: under 12 months. >24 months is concerning. Formula: CAC / (ARPU × Gross Margin / 12). NRR helps payback indirectly - the longer customers stay, the less the payback period matters.
CAC / (Monthly ARPU × Gross Margin)$20K CAC / ($1K monthly ARPU × 80% margin) = 25 months.
See how public B2B SaaS companies disclose this metric, with full historical time series.