The reconciliation between top-down and bottom-up TAM/SAM/SOM estimates is a critical credibility check. If both methods converge within 20-30%, your estimates are robust. If they diverge significantly, you need to investigate why and adjust assumptions.
If top-down says €1B and bottom-up says €100M, one of your assumptions is wrong. Find and fix it before presenting to investors.
Common reasons for divergence: (1) Top-down includes adjacent markets you can't serve, (2) Bottom-up underestimates total customers, (3) Price points differ between approaches, (4) Geographic assumptions are inconsistent.
Key Takeaways
- Cross-validate top-down and bottom-up estimates.
- Convergence within 20-30% = credible estimates.
- Large divergence means an assumption is wrong — find and fix it.
- The bottom-up SOM is usually the binding constraint for startups.