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Top-Down Demand Market Sizing Framework
The most popular market sizing technique for consumer goods, digital applications, and retail products. Start with total population and apply sequential demographic filters.
Core Equation: Market Size = Total Population × Target Demographic % × Target Income % × Penetration Rate × Annual Frequency × Price per Unit
Summary:
The Top-Down approach begins with a large macro population (e.g. 335M US citizens) and systematically narrows down through MECE demographic filters (age, income, urban vs rural, user behavior) to reach the active addressable customer base.
When to Use vs When to Avoid
WHEN TO USE:
• Mass-market consumer goods (smartphones, apparel, soft drinks).
• Digital subscriptions & mobile apps (streaming services, dating apps).
• Services with broad demographic appeal (gym memberships, food delivery).
WHEN NOT TO USE:
• Physical brick-and-mortar retail stores with fixed checkout capacity (use Supply-Side instead).
• B2B enterprise software with pricing based on corporate headcount (use B2B Segmentation).
Step-by-Step Execution Framework
Step 1: Select Appropriate Base Population Unit
Decide whether the buying unit is an individual (smartphones, sneakers) or a household (refrigerators, WiFi subscriptions, cars).
Formula: Unit = 335M Individuals OR 130M Households
Pitfall: Using individuals for household goods, inflating your market size by 2.5x–3x.
Step 2: Apply Demographic & Age Filters
Isolate the target age group (e.g. 18–35 for college/young professional products; 65+ for senior care).
Formula: Target Age Cohort = 335M × 25% = 84M people
Pitfall: Creating overlapping age segments that violate MECE principles.
Step 3: Filter by Income & Willingness to Pay
Adjust for economic affordability (e.g. luxury items target the top 20% of households earning >$100k).
Formula: Qualified Buyers = 84M × 30% middle/upper income = ~25M potential buyers
Pitfall: Assuming 100% of an age group can afford premium or discretionary purchases.
Step 4: Apply Annual Frequency & Pricing
Multiply active buyers by annual consumption frequency and average price per unit.
Formula: Total Revenue = 25M users × 4 purchases/year × $50 = $5 Billion TAM
Pitfall: Forgetting to convert weekly or monthly frequencies into annualized totals.
MBB Partner Advice & Scoring Focus
Partner Tip: Always round intermediate numbers to clean, round figures with the interviewer’s permission (e.g., "May I round 335M to 330M for simpler calculation?").
Scoring Focus: Interviewers look for clear verbal labeling of each filter before doing the arithmetic.
Pros & Cons of This Method
PROS:
+ Logical and intuitive for interviewers to follow.
+ Easy to defend assumptions using standard demographic benchmarks.
CONS:
- Can lead to compounding estimation errors if too many subjective percentages are multiplied in series.
Frequently Asked Questions
Q: When should I use Top-Down vs Bottom-Up in a case interview?
A: Use Top-Down when market demand dictates volume (consumer products with infinite shelf capacity). Use Bottom-Up when physical supply or operational capacity dictates volume (restaurants, airports, stadiums).
Frequently Asked Questions
When should I use Top-Down vs Bottom-Up in a case interview?
Use Top-Down when market demand dictates volume (consumer products with infinite shelf capacity). Use Bottom-Up when physical supply or operational capacity dictates volume (restaurants, airports, stadiums).
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