Top-down market sizing starts with a large industry figure and assumes a share. Bottom-up sizing counts real customers and prices. Only the second tells you anything reliable.
12 min read · Level 3
I have come to treat a top-down market slide as a small negative signal rather than a neutral one. Not because large markets do not matter, but because founders who have done the harder bottom-up work almost always lead with it, and the absence of it usually means nobody has yet counted the customers.
Top-down sizing takes an industry figure and claims a slice:
Global healthcare software market 50,000,000,000 "If we capture just 1%" 500,000,000 of revenue
It sounds modest and says almost nothing. There is no reason given for 1%, no definition of which customers, and no link to how the company will reach them.
Bottom-up sizing counts who would actually buy and at what price:
Independent dental practices in the target country 40,000 Annual price per practice 3,600 Total market at full adoption 144,000,000
Then it asks what share is realistically reachable. If the company could win 10% of practices in five years:
4,000 practices x 3,600 = 14,400,000 of annual recurring revenue
That is a smaller number and a far more useful one. It can be tested: is 40,000 the right count, will practices pay 3,600, how many can a sales team reach per year?
A good bottom-up analysis also names the next market the company could expand into, and why its product and relationships would carry over.
Because the top-down version cannot be wrong in a way anyone can check, which is exactly why it appears in so many pitches. It is a narrative, not a measurement.
Bottom-up sizing exposes the assumptions: customer counts, price, reachable share, sales capacity. When one is weak, you know precisely where the risk is.
And for a venture-style return, the market needs to support a large outcome. Bottom-up sizing shows honestly whether it can.
Educational, not personalised financial advice. Nothing in the Investor Academy is a recommendation to buy, sell or hold anything — what is right for you depends on your own circumstances and the rules where you live.
Testing the bottom-up numbers. The investor checks each input.
Assumption Pitch Checked Adjusted Target practices 40,000 only 28,000 are independent, not chains 28,000 Annual price 3,600 current customers pay 2,400 on average 2,400 Five-year share 10% unchanged 10%
Adjusted five-year revenue: 2,800 x 2,400 = 6,720,000
The realistic five-year figure is under half the pitch's 14,400,000. The business may still be good, but the investor now knows it needs either a larger market, a higher price or expansion into chains to become a large company.
Accepting a top-down market figure with an assumed small share as evidence of a large opportunity.
Count the specific customers who fit, multiply by a realistic price, and compare with any top-down figure presented.
Verify customer counts from primary sources and price from what current customers actually pay.
Ask how many customers the team can realistically win per year, and whether that supports the claimed share.
Ask where growth comes from after the first segment, and why the company would win there too.
Whenever a startup presents a market size or revenue ambition.
Do not treat bottom-up figures as precise. They are more honest than top-down ones, but still built on estimates that should be stress-tested.
Early-stage investors commonly describe reviewing pitches where the headline market size, often taken from an industry research report, bore little relation to the specific customers the product could serve, and where bottom-up counts later showed a much smaller reachable market.
The number that matters is the one built from customers you can name, at prices they already pay.
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