Build a bottom-up market model

This lesson is part of the saas market sizing course. Estimate demand from eligible accounts and defensible spending assumptions while keeping evidence separate from scenarios.

Prepare your working case

Choose one product and one customer segment. Gather the relevant product information, customer evidence and operating records before writing the answer. If you are learning without access to a business, use a clearly labelled practice case and state the assumptions you make.

Keep the scope small enough that you can explain the decision to another person. The purpose is to learn how to reason through the work, not to produce a longer document than the situation needs.

Work through the exercise

Step 1

Find a source for the population matching the market definition.

Record your answer, the evidence behind it and any unresolved dependency before moving to the next step.

Step 2

Apply eligibility filters with documented reasoning.

Record your answer, the evidence behind it and any unresolved dependency before moving to the next step.

Step 3

Estimate annual spending using comparable offers or buyer evidence.

Record your answer, the evidence behind it and any unresolved dependency before moving to the next step.

Step 4

Calculate base, low and high cases with independent assumptions.

Record your answer, the evidence behind it and any unresolved dependency before moving to the next step.

Worked situation

A count of 5,000 eligible firms and an assumed $6,000 annual spend produces a $30 million theoretical opportunity, not a company revenue forecast.

Treat this as an illustration of the decision, not a measured result or a claim that the same approach fits every company. In your own case, identify which condition would make the conclusion different. That condition belongs beside the recommendation.

Produce the deliverable

A model with account counts, spending assumptions, sources and scenario ranges.

Use the working template to organize the result, then run the review checklist. Add the project name, date, owner and a link to supporting evidence. If a key input is unknown, describe how you would learn it rather than filling the gap with a confident guess.

A useful deliverable can be read without a live presentation. Another person should be able to identify the problem, understand the recommended choice and see what happens next. Remove any section that does not help them make or execute that decision.

Review your work

Ask a colleague to challenge the weakest assumption. Write down the strongest alternative explanation and the evidence that would distinguish it from your current view. This makes the result easier to revise when new information arrives.

Continue the course

Return to the course outline or use the lesson navigation below. For the wider topic, visit saas market. The resource library and calculators provide additional working tools.

Apply build a bottom-up market model in a working review

Use the lesson to produce a small working artifact. State the starting problem, apply the method to one case and ask another person to inspect the result. Compare their interpretation with the explanation you intended. Revise the artifact before repeating the exercise at a larger scope; reading the material alone does not establish that the method can be applied.

For this topic, involve the research owner and the person using the estimate for a decision and work from source method, market boundary and assumption table. The relevant unit is a clearly defined population, period and value measure. State the question the review should resolve before choosing a chart, an asset or a tool. If participants disagree about the unit or scope, resolve that disagreement before combining their evidence.

Evidence to prepare

Read the original definition before combining figures. Publication date, collection period and forecast horizon answer different questions. A market estimate can be useful without being directly comparable to another publisher’s number.

Two situations that can change the interpretation

When competitor count is treated as demand

A crowded category may contain many small tools serving different jobs rather than one homogeneous market.

Use this check: Separate evidence of supply from evidence of customer problems, spending and switching behavior. Few competitors can indicate opportunity or lack of demand; the count alone does not decide.

The focused diagnostic guide provides the correction process and a working evidence sheet.

When TAM has no eligible-account rule

Not every company in an industry needs or can adopt a particular operational workflow.

Use this check: Define the customer workflow, geography, supported requirements and exclusion criteria. A large addressable market is not evidence of obtainable demand.

The focused diagnostic guide provides the correction process and a working evidence sheet.

Record the decision and the limit

A software-revenue estimate and a broader customer-spending estimate may both be credible within their own definitions. Averaging them does not create a better answer. Explain the boundary and choose the measure that matches the decision being made.

Keep the conclusion beside the evidence that supports it. Record what the team will do, who owns the next action and which event or date will trigger a review. If the underlying definition, audience or product behavior changes, revisit the conclusion rather than assuming the old result still applies. A clear limit is useful information; it tells the next reader where additional investigation is required.

Use the complete topic collection for related methods and the category field guides when the product’s buying situation or implementation requirements change how the method should be applied.