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
Best for

Founders and operators who need one starting point for CAC, LTV, payback, margin, burn, and runway together.

Decision

Where to start when growth quality, burn efficiency, and capital planning all interact.

Use it when

You want a practical entry page that links the right calculators and guides before building a broader operating review.

Reviewed by

MetricKit editorial review for SaaS planning workflows.

Reviewed to keep the entry path task-oriented so users can move from headline metrics into the next calculator or guide with less guesswork.

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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)