Why most SaaS founders calculate CAC payback wrong (and a free client-side tool I built to fix it)
Hey Indie Hackers,
A common issue I kept seeing across SaaS communities—and one I’ve wrestled with myself—is how unit economics are calculated in early-stage software businesses.
Too often, founders use the "classic" quick formula:
$$\text{Payback} = \frac{\text{CAC}}{\text{Monthly Revenue}}$$
The problem? If you have an 80% software gross margin after hosting, support, and third-party APIs, your true cash payback is actually 25% longer than that naive math suggests. Ignoring monthly logo churn and gross margin drag leads to unexpected cash runway crunches.
Most founders end up building messy, one-off Google Sheets where formulas break as soon as you want to compare scenarios.
To solve this, I built Best SaaS Metrics—an interactive CAC Payback, LTV:CAC, and unit economics engine built specifically for subscription businesses.
What it does:
Gross-Margin & Churn-Adjusted Modeling: Calculates true recovery periods based on net contribution rather than top-line revenue.
36-Month Cumulative Cash Flow Trajectories: Visualizes the actual curve of upfront customer acquisition costs versus cash recovery, factoring in monthly churn over time.
Niche-Specific 2026 Benchmarks: Includes pre-configured baselines for Bootstrapped Micro-SaaS, PLG Self-Serve, DevTools, and Enterprise B2B SaaS based on public datasets (Bessemer, KeyBanc).
100% Client-Side & Privacy-First: No database persistence, no tracking scripts capturing your numbers, and no mandatory email signups. All calculations run in your browser.
Scenario Comparison & Export: Lets you test multiple growth levers side-by-side and export your breakdown to PDF.
Why I'm sharing it here
I built this tool to provide clean, transparent benchmarks for bootstrapped and indie founders without gating it behind a sales demo or newsletter wall.
You can try it out here: bestsaasmetrics.com
I would appreciate feedback from fellow builders:
Does the churn-adjusted payback model align with how you model unit economics internally?
What additional calculators would be most useful (e.g., Net Revenue Retention, Rule of 40, or Burn Multiple)?
Happy to answer questions about the tech stack, the math, or the benchmark data!
