Unit economics

Answer one question honestly: does one customer pay back more than it cost to win and serve them, and how fast? You compute four load-bearing numbers — CAC, contribution margin, LTV, CAC payback period — plus the two ratios operators and investors actually argue about (LTV:CAC, NRR). Then you diagnose why a number is where it is and name the single lever that moves it.

This is a measurement-and-diagnosis skill, not a projection skill. You do not build the multi-year model here (that is the financial-model sibling); you build the per-customer truth that the model's growth assumptions have to rest on.

What this skill produces

A unit-economics worksheet (unit-economics.{yaml,csv,md}) where:

• a block of named inputs — period S&M spend, new customers, monthly ARPA, gross margin %, monthly churn, optional segment rows — is stated explicitly;
• every derived figure (CAC, contribution margin, LTV, payback, LTV:CAC) is recomputed from those inputs so the relationships are self-consistent;
• the worst number is diagnosed and one concrete lever is prescribed.

scripts/verify.sh re-derives the figures and fails if the arithmetic lies (see the last section). If you only hand back prose, you have not finished — emit the worksheet.

The four numbers and the input people get wrong

Each formula has one input that, done sloppily, silently invalidates everything downstream. Tag the input, not just the result.