2.2
Product-Market Fit / The 40% Test
A survey rule of thumb: ask users how they would feel if they could no longer use the product, and treat 40% answering “very disappointed” as the threshold for fit.
Sean Ellis (2009), from growth practice rather than from research
What it does
Gives a pre-scale team one number to argue about and a reason not to spend on growth until it moves. As a stop sign it is useful: it converts “do people want this?” from an argument into a measurement a team can repeat monthly.
When it breaks
The 40% threshold has no published derivation. It is a remembered benchmark from a small set of startups, not an estimate with an interval around it. Worse, the survey only reaches people still using the product, so it measures the enthusiasm of survivors and is structurally silent on everyone who already left. A product with a small, devoted, unscalable audience passes it comfortably; that is the exact failure mode it is meant to catch.
Case
Kromatic documents the false-positive pattern: teams clearing 40% among a narrow retained cohort, concluding they had fit, scaling spend, and finding the score collapse as acquisition reached beyond the initial audience. The test never sampled the people who churned.
Kromatic · Why the 40% test gives false positives ↗In the wild
Unchecked · not part of the tier
What people have written about this tool in the last twelve months. A machine found these and nobody has read them. Everything above this line was checked by hand.
Loading…