Sean Ellis's 40% Rule
When 40% of your users would be 'very disappointed' to lose the product, the signal for product-market fit is strong enough to scale acquisition.
Why PMs should care
This is the most useful product-market-fit signal available to a working PM. It's cheap (a one-question survey), it works without special tooling, and it gives you a clear target.
The magic number 40 isn't a pass/fail line. It's a threshold Ellis calibrated by watching a lot of companies. Treat your current score as a distance to close, not a grade to pass.
More useful than the headline number: segment the 'very disappointed' responses. Who are they? What do they have in common? What job are they hiring the product for that the other users aren't? That analysis is worth more than the overall percentage, because it tells you exactly where your real product-market fit lives — and therefore what your positioning and acquisition strategy should focus on for the next year.
Example in product work
A team runs the Ellis survey on their 90-day active users:
- 32% very disappointed
- 41% somewhat disappointed
- 27% not disappointed
The headline ('we're close but not there') is less useful than what the PM does next: split the 32% by usage pattern.
It turns out 78% of the 'very disappointed' cohort are users who placed their first recurring investment in the first 14 days of signup. These users have, on average, 3.2× the 90-day deposits of the rest.
The team stops trying to move the overall number and instead focuses the next two quarters on getting more users to place a recurring investment in their first two weeks. Eighteen months later, the overall 'very disappointed' number is 44% — not because the product got better for everyone, but because more users got pulled into the pattern that was already producing fit.
What to do when you see it
- It's the most useful PMF signal for a working PM — cheap to run, survey-based, gives you a target to hit.
- 40% isn't a hard pass/fail line. It's a calibrated threshold from watching many companies. Treat your current number as a distance to close.
- The most valuable move is to segment the 'very disappointed' responses — who are they, what do they share, what job are they hiring the product for?
- That segmentation often matters more than the headline number. It tells you where your actual fit lives.
Sources & further reading
- Using Product/Market Fit to Drive Sustainable Growth — Sean EllisSean Ellis's original article describing the 40% test and how to run it.
- How Superhuman Built an Engine to Find Product/Market Fit — First Round ReviewRahul Vohra's widely-cited case study applying and extending Ellis's 40% survey at Superhuman.