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Framework

The 40% Rule (Sean Ellis PMF Test)

Survey users: 'How would you feel if you could no longer use this product?' If 40%+ say 'very disappointed,' you have PMF.

Origin: Sean Ellis, ex-Dropbox/LogMeIn growth lead. Adopted as the de facto YC PMF benchmark.

The question cuts through the lying. Users will say 'I love it!' to your face. They will not invent fake disappointment in an anonymous survey.

The 40% threshold is empirical — Sean ran the survey across 100+ startups and found that the ones who crossed 40% almost always went on to scale. Below 40%, almost none did.

Run it as soon as you have ~50 users who've used the product more than twice. Re-run quarterly. Watch the number move.

Steps

  1. 1. Define qualified user

    Used the product 2+ times in the last 30 days.

  2. 2. Send the survey

    Single question + optional follow-ups (what type of person benefits, what's the main benefit, how to improve).

  3. 3. Calculate %

    Of all respondents, % who answered 'very disappointed.' Aim for 40%+.

  4. 4. Read the qualitative

    The 'very disappointed' segment tells you exactly which users to acquire more of.