Unit economics hub: CAC, LTV, payback, and runway (a practical stack)

A practical hub for unit economics: CAC, fully-loaded CAC, LTV, payback, margin impacts, burn multiple, and runway planning.

Updated 2026-01-28

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How to use this hub

Unit economics isn't one number. Use this hub to connect acquisition cost (CAC) to cash recovery (payback), then sanity-check sustainability with burn multiple and runway. Start simple, then add realism with fully-loaded costs and sensitivity analysis.

The unit economics stack (what to compute first)

StepComputeWhy it matters
1CAC (and fully-loaded CAC)True cost to acquire customers, not just ad spend
2LTV (cohorted if possible)Ceiling for how much acquisition you can afford
3LTV:CACQuick sanity-check for profitability potential
4CAC paybackCash constraint lens (can you fund growth-)
5Burn multiple + runwayAre you buying growth efficiently, and for how long-

A fast operating workflow

  • Choose a primary segment (SMB vs enterprise) and compute CAC/LTV/payback per segment.
  • Use fully-loaded CAC for board-level truth; use paid CAC for channel optimization.
  • Run payback sensitivity when ARPA and margin are moving (pricing, COGS, mix).
  • Translate improvements into cash runway impact (growth is constrained by cash).

What 'good' looks like (rule-of-thumb, not law)

  • LTV:CAC around ~3:1 is a common target; earlier-stage teams often accept lower if growth is strong and payback is short.
  • Payback targets depend on cash and retention: shorter payback is safer, especially with volatile channels.
  • Burn multiple trends are often more actionable than a single month's value.

Common mistakes

  • Mixing gross margin and contribution margin (be consistent about variable costs).
  • Using blended CAC for a single channel decision (blend hides allocation effects).
  • Assuming churn stays constant after pricing changes (recompute cohorts).
  • Treating LTV as precise; always scenario-test with sensitivity ranges.

FAQ

Should we use fully-loaded CAC or paid CAC-
Use fully-loaded CAC for strategic decisions and investor/board reporting. Use paid CAC for channel optimization, but keep the definitions consistent.
If LTV:CAC is great, why can we still be cash negative-
Because payback timing matters. A strong LTV doesn't help if it takes too long to recover CAC and you run out of cash first.

More in saas metrics

Unit economics: CAC, payback, LTV, and LTV:CAC (how to model them)
UTM + GA4 attribution: practical tracking for paid ads (without lying to yourself)