# How do we calculate a credible TAM for a B2B software company?

Build it bottom-up from a counted account universe that matches your ICP definition, priced at your actual realised ACV by segment — not top-down from an analyst market figure. A TAM you can enumerate is a target list; a TAM you can only cite is a slide.

The bottom-up version has a second payoff: the same scored universe becomes the territory input and the outbound target list, so the work is reused rather than done once for a fundraise. State the counting method and the ACV basis alongside the number.

## Sources

- **Method** — [Market Map playbook — Ways to value a potential account](https://www.leanscale.team/knowledge/playbooks/market-map-playbook/)

---
Cluster: Icp · https://www.leanscale.team/knowledge/answers/calculate-tam-b2b/