The Sean Ellis Test

What it is

The Sean Ellis test is the most widely used method for measuring product-market fit. Growth expert Sean Ellis, after running it across hundreds of startups, found one survey question that reliably separated companies that would go on to grow from those that would stall. It is the instrument PMFtracker is built around.

This page is the quick reference. For the full method, the story behind the 40% number, and worked benchmarks, read the complete guide: the Sean Ellis 40% rule, explained. To run it in minutes, use the ready-made survey template or the free PMF score calculator.

When to use it

• To measure whether you have PMF today. It is the fastest honest read available.
• To track fit over time. The score is a leading indicator; watch the trend, not one number.
• After users are activated. Only people who have felt your core value can answer meaningfully.

How to apply it

1. Survey only engaged users. Ask people who have recently experienced your core value, not sign-ups who never came back. Surveying the wrong people is the number one way scores go wrong.
2. Ask the one question. "How would you feel if you could no longer use [product]?" with four options: very disappointed, somewhat disappointed, not disappointed, and N/A.
3. Calculate the score. Very disappointed divided by the sum of very, somewhat, and not disappointed, times 100. The N/A bucket is excluded.
4. Compare to 40% and segment. At or above 40% signals fit. Then segment the score to find the group that loves you most.
5. Track it over time. A single reading is a snapshot. Tracking the trend tells you whether you are moving toward fit or away from it.

Example

Superhuman is the canonical case. Its early Sean Ellis score was 22%, well below the bar. Rather than guess, the team used the survey to segment users, doubled down on the people who loved it, and walked the score to 58%. Slack, when it measured, came in at 51%. The number is not just a grade, it is a map of who to build for. See how Superhuman did it.

Common mistakes

• Surveying everyone, including inactive users. Only engaged, activated users give a meaningful answer.
• Too few responses. Below roughly 40 valid responses the score swings wildly. See how many you need.
• Treating one reading as final. The score is a trend to track, not a one-time grade.

How it connects to your PMF score

The Sean Ellis test does not just relate to your PMF score, it is your PMF score. Every other framework here, from Jobs to Be Done to the beachhead, is a way to move this number. The test is how you find out whether the moves worked.