Meaning and transaction use
UK government investor-readiness guidance asks companies to evidence TAM, SAM and SOM with credible, data-backed analysis and to show who customers are, where they are and how they buy. [S1]
A UK innovation-funding assessment defines TAM as total market demand and the maximum revenue opportunity at 100% share. It expects an evidence-based assessment and treats unsupported estimates as weak. [S2]
Proposed control method: preserve every source, date, unit, inclusion rule and conversion step; reconcile top-down and bottom-up methods; and update the model when price, eligibility or demand evidence changes.
Worked example
Illustrative market sizing only. Assume 80,000 eligible organisations, annual demand of four units each and a price of USD 500 per unit. Assume no overlap or churn adjustment.
Scroll the table horizontally to view all columns.
| Measure | Calculation | Result |
|---|---|---|
| Annual units | 80,000 x 4 | 320,000 |
| TAM | 320,000 x USD 500 | USD 160 million |
| Revenue at 1% share | 160 million x 1% | USD 1.6 million |
| Revenue at 5% share | 160 million x 5% | USD 8 million |
The assumptions produce a USD 160 million TAM. The share scenarios are arithmetic illustrations and do not establish obtainable demand, growth or valuation.
Proposed transaction review process
Set the boundary
Define customer, need, product, geography, unit, price and date.
Build bottom-up demand
Count eligible buyers and apply evidenced usage and pricing.
Cross-check
Compare with credible industry, customer and transaction data.
Monitor
Track changes in eligibility, price, adoption and realised customer demand.
Evidence checklist
Customer universe
Dated registries, customer lists and documented inclusion rules.
Demand evidence
Purchasing data, surveys, contracts and observed usage.
Pricing evidence
Invoices, price lists, contracts and comparable offers.
Model record
Sources, assumptions, exclusions, currency and sensitivity cases.
Decision framework
| Situation | Proposed action |
|---|---|
| Customer counts overlap | Deduplicate before aggregation. |
| Price varies by segment | Model segments separately and reconcile the weighted result. |
| A source is management-estimated | Label it and test independent evidence and downside cases. |
| TAM grows while sales do not | Test serviceability, adoption, competition and execution rather than expanding the boundary. |
Common errors to check
- Presenting TAM as forecast revenue.
- Multiplying incompatible units or periods.
- Using an industry total that includes unserved products or geographies.
- Reporting a precise figure without sources and sensitivity analysis.
Test the market boundary
Bring the customer universe, demand evidence, pricing and market model to a TAM review. Reconcile every unit and source before using the result in fundraising or valuation.
Discuss the transactionPrimary references and editorial scope
- GOV.UK: Investor Readiness Essentials
Evidence-backed TAM, SAM and SOM and customer-market definition. Reference checked 17 September 2026. - Innovate UK: Estimate the realistic market opportunity
TAM definition and evidence expectations. Reference checked 17 September 2026.
General venture-capital education. Figures and shares are hypothetical. Market boundaries, demand, pricing, growth and obtainable share require transaction-specific evidence.
General business information. Obtain advice appropriate to the legal, tax, accounting and financing facts. No offer, lender commitment or transaction outcome is represented. All worked examples use expressly assumed figures. Editorial draft date: 17 September 2026.
