I've analyzed unit economics for 50+ SaaS companies as a fractional CFO.
Here are the three metrics that consistently trip up founders — and how to get them right.
1. Blended LTV (wrong) vs Gross-Margin-Adjusted LTV (right)
Most founders just do ARPU / churn. But that ignores COGS and support costs.
Gross-margin-adjusted LTV = (ARPU × Gross Margin %) / Churn Rate. For a $100 MRR customer with 80% gross margin and 5% churn:
LTV jumps from $2,000 to $1,600 — a 20% difference that changes fundraising narratives.
2. One-size-fits-all CAC (wrong) vs Channel-Specific CAC (right)
Blended CAC hides which channels destroy value. Paid CAC might be $800 with 6-month payback,
while organic CAC is $150 with 1.5-month payback.
If you only track blended ($350), you might double down on paid ads that actually underperform.
3. Simple Payback (wrong) vs Breakeven Including Support (right)
Support cost per customer often equals 15-25% of MRR. Include it:
Real Payback = CAC / (MRR - COGS - Support Cost).
A "3-month payback" becomes 5 months when you account for support — which changes hiring decisions.
The Fix: I built a free Google Sheets calculator that does all three correctly.
It includes pre-built formulas, sample cohorts, and a board-ready summary sheet.
Grab the template at microtoolsb2b.gumroad.com/l/saas-unit-economics (free with email signup).
Tags: Google Sheets, SaaS metrics, unit economics, LTV/CAC, startup finance
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