"How to Calculate CAC Payback Period (the Right Way)" — CJ Gustafson (Mostly Metrics)

Why this is in the vault

CAC Payback is the metric CJ recommends as the LTV/CAC replacement (per the Nickelback piece). This is the operating mechanics of how to compute it correctly — gross-margin adjustment, sales-cycle lagging, segmentation by funding stage. If I'm going to push CAC Payback as the MAC discovery question, I need to be able to ask it the right way. This piece is the spec.

⚠️ Sponsorship

Sponsored by Mercury (fintech for startups). Mercury's audience overlap with Mostly Metrics is essentially perfect. No editorial bend — the calculation mechanics are universal.

Core thesis

CAC Payback Period is the months-to-recoup-customer-acquisition-spend metric, and it's frequently miscalculated in three ways that all make it look better than reality. The fix is (a) adjust the numerator for gross margin, (b) lag the denominator for the actual sales cycle, (c) segment by ARR cohort and funding stage rather than blending.

The calculation, done right

CAC Payback (months) = CAC / (New MRR × Gross Margin %)

With two corrections most people skip:

Numerator (CAC): Lag the sales-and-marketing spend by the sales cycle. Enterprise = 180 days, mid-market = 90 days, SMB = 30 days. The spend that closed today's customer happened months ago.
Denominator (MRR): Multiply by gross margin %, not by raw revenue. You're recouping cash, not revenue, and COGS isn't free.

Benchmarks by stage

Private software, all stages blended: <18 months target
Larger public enterprises: 24+ months acceptable
Insurance / wealth management vertical: very different shape (longer payback, higher LTV)
Mobile / e-commerce: very different shape (shorter payback, lower LTV)

Voice tactics

"You can't trade a buck for eighty-five cents forever." Concrete-dollar reframing of an abstract concept. Sticky.
"Deadbeats!" applied to newly hired unbilled GTM staff. Comic exaggeration. The "deadbeats" framing is the kind of move SC could pick up — taking an unflattering-sounding word and applying it self-deprecatingly to a structural-not-personal phenomenon.

Mapping against Ray Data Co

MAC discovery script. When MAC engages a portfolio company, "what's your CAC Payback Period, computed with gross margin adjustment and sales-cycle lagging" is a much sharper discovery question than "what's your CAC." It immediately reveals whether finance is doing the work or hand-waving. If they can't answer in those terms, the engagement should start with metric hygiene before AI cost optimization.
For Squarely. Squarely's CAC is mostly organic (App Store search, X mentions, no paid spend). CAC Payback for organic acquisition is degenerate — payback is immediate because spend is ~0. But this also means we have no CAC discipline ready if/when we start paid acquisition. The first paid-spend dollar should come with a CAC Payback model attached.
For Sanity Check growth. Same shape — currently organic. The moment we start paid newsletter growth (LinkedIn ads, sponsored placements), the gross-margin-adjusted CAC Payback model applies. Margin for newsletter is high (≈90% after platform cost), so the calculation should be straightforward.
General lesson on metric-calculation discipline. The pattern CJ keeps surfacing across pieces: most operating metrics are miscalculated by default. The right move isn't to add more metrics, it's to compute fewer metrics correctly. I should apply this to my own dashboarding: rather than tracking 12 vanity metrics for SC growth, track 3 done right (CAC Payback, NDR-equivalent, decision-throughput).

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mostlymetrics cac payback calculation