How CAC payback is calculated
CAC payback = CAC ÷ (ARPU × gross margin %). It's the number of months a single customer takes to repay the cost of acquiring them, on a gross-profit basis. Net-revenue payback (ignoring margin) overstates capital efficiency — gross margin is the version that matters.
Benchmarks (2024 SaaS)
- Under 12 months — capital-efficient. Channel is scaleable. Series A bar.
- 12–18 months — workable for SMB SaaS with sticky retention. Watch CAC inflation.
- 18–24 months — risky. Requires > 90% logo retention to amortize the spend.
- Over 24 months — unsustainable for non-enterprise SaaS. Cut spend or raise ACV.
LTV : CAC ratio
LTV (gross-margin) = ARPU × gross margin ÷ monthly churn rate. The ratio LTV:CAC tells you the lifetime profit multiple per dollar spent on acquisition. The classic David Skok bench is 3:1 minimum, with 5:1+ signaling under-investment in growth.
When this calculation breaks
LTV from a static churn rate overstates long-tail value when cohorts decay non-linearly (true for most SaaS). For investor-grade reporting, use cohort-based LTV from your billing data — but as a sanity check on whether to scale a channel, this is the right back-of-envelope.
Channel-level vs. blended
Blended CAC hides channel-level dysfunction. If you're running paid + content + partnerships, calculate payback per channel — the worst channel is usually subsidizing reported numbers. Drop the bottom-quartile channel and reallocate.
Companion tools
CAC payback assumes the LTV math is real — validate the underlying retention curve with the Cohort Visualizer before you trust flat-churn LTV, grade the recurring-revenue base feeding CAC with the MRR Health Snapshot, project acquisition spend against your cash position with the Runway Calculator, and check whether the payback profile clears the band you're raising into with the Fundability Scorecard.
Related reading
Background on the recurring-revenue base CAC payback assumes: MRR vs ARR for bootstrapped founders. Cash-side context if your CAC is forcing a runway decision: The SaaS Runway Playbook.