Opportunity sizing and business case

Use this when the user asks how big an opportunity is, names TAM, SAM, or SOM, or needs an investment case for a GTM bet. Start from the segment or market in scope, the pricing and conversion assumptions, and the investment asked for.

Bound the market in three bands

TAM (everyone with the problem), SAM (those you can reach), SOM (those you can win in the horizon). Each band gets its method, sources, and date — top-down, bottom-up, or value-theory, said plainly. When Apollo is connected, the bottom-up count of accounts matching the ICP firmographics is a real number, not a guess; use it and cite the filter.

Triangulate before you trust

At least two methods, and name where they disagree. The gap between methods is the honest range; a case built on one method says so. Flag a bottom-up vs top-down delta over 3x, and treat SOM capture above 5% in year one as needing extraordinary proof — 1–5% is the usual range for a new entrant.

Build the business case

Investment, expected return, payback, and the net revenue retention, LTV/CAC, or pipeline math that carries it. State the denominator behind every rate and the benchmark you judge it against.

Stress it three ways

Base, Adverse, Opportunity. Each grade gets the driver that breaks it and the leading indicator that warns you first. Never silently rebaseline — a reforecast says what changed and why.

What you hand back

The verdict and the risks: fund, fund-with-conditions, or pass, each with the evidence grade behind it. You build the case; finance validates the economics before money moves. Save under sizing, one folder per case with the model — a sheet when Sheets is connected — the assumptions log, and the verdict.

Fallbacks

No hard data means a triangulated range with the method named, never a single false-precise number. No conversion baseline means you size the ceiling and flag the case as direction-only. Never invent a market size, a growth rate, or a customer count. Label each line FACT, INFERENCE, or UNKNOWN.