Financial Planning
Bottom-Up Market Sizing: A Startup TAM Worksheet
Build a bottom-up startup market estimate from customer counts and revenue assumptions. Use a source register and a copyable TAM worksheet.
What you will learn
- Define a countable customer unit
- Build a sourced market calculation
- Keep total opportunity separate from an initial sales plan
Bottom-up market sizing estimates an opportunity from a defined customer count and a realistic revenue assumption. Start with who could buy, what they would buy, and how you count them. A large industry number is not a substitute for a defensible customer calculation.
Choose the unit before doing the math
Decide whether you sell to companies, locations, seats, households, or transactions. Avoid multiplying a count of organizations by a price per seat without estimating seats per organization. Set geography, business size, and relevant operating requirements before looking for a source. This makes exclusions visible.
Illustrative annual opportunity = eligible customer units × annual revenue per unit
Document: unit, eligibility definition, geography, source date, and pricing assumption.Worked example: a location-based product
A fictional scheduling startup investigates 12,000 eligible clinic locations. This is an invented count for teaching, not a market estimate. Its assumed annual price is $2,400 per location.
| Layer | Illustrative calculation | What it means |
|---|---|---|
| Defined total opportunity | 12,000 × $2,400 = $28.8M annually | A modeled market at the assumed price |
| Initial serviceable segment | 3,000 × $2,400 = $7.2M annually | Locations matching the initial product and geography |
| First-year operating hypothesis | 40 wins × $2,400 = $96,000 annualized revenue | A sales hypothesis; not the market size |
The 40-win hypothesis needs a separate acquisition model: reachable buyers, meetings, conversion, and timing. Do not choose a tiny market percentage and call it a sales plan. Annualized contracted revenue is also different from cash collected in the first year.
Build your source-and-assumption register
| Input | Source or test | Review question |
|---|---|---|
| Customer count | A dated official dataset or clearly defined directory | Does it count businesses, establishments, or people? |
| Eligible share | Documented filter or an explicit hypothesis | Can you explain the exclusion without double-counting? |
| Annual price | Current contracts or a labeled pricing test | Is this observed willingness to pay or an assumption? |
| Expansion segment | Separate geography or customer group | Is it incremental, or already in the total? |
For US business counts, the Census Bureau’s Statistics of U.S. Businesses is a useful source to investigate. Check the dataset’s definitions and coverage; not every business is an addressable buyer for your product.
Pressure-test the result
- Recalculate with a lower price and narrower eligible count. Show which input changes the answer most.
- Check for duplicate locations, overlapping customer groups, and annual-versus-monthly units.
- Write down what your current product cannot serve yet. Keep future expansion separate.
- Ask a teammate to reproduce the calculation using the linked inputs.
Customer unit: [definition]
Market boundaries: [geography + segment]
Count: [number, source URL, date, coverage]
Annual price: [amount, evidence or hypothesis]
Modeled opportunity: [calculation]
Initial segment: [count + exclusions]
Next validation: [input, owner, date]Further reading: US Census Statistics of U.S. Businesses.
Put the lesson to work
Keep the source register beside your pitch. A reader should be able to distinguish the opportunity from your current customer evidence. Explore Finta Academy.
A Finta Field Guide based on our Fundraising Academy teaching. Worksheets and fictional examples are original educational exercises, not customer results or personalized financial, legal, or tax advice.