How do you measure product-market fit?

Sean Ellis's 40% rule: Survey active users on disappointment without your product. Pair with retention curves and organic growth.

What is the 40% rule for PMF?

40%+ of recent users say they'd be "very disappointed" sans your product. Empirical benchmark from 100+ startups.

No — it's intent, not behavior. Use above 50 as a signal, but retention rules.

Never. Organic growth first, or watch cash vanish.

🧠 Engineering Culture

Retention flat at week 4? Users ghosting? That's no PMF. Here's the hard data and checklist to know for sure – before you scale into oblivion.

DevTools Feed Apr 03, 2026 4 min read 17 views

Hit 40% on Sean Ellis survey for PMF green light — test active users only. 𝕏
Week-4 retention flattening trumps all surveys; it's the ultimate behavior test. 𝕏
PMF spectrum: Nail one segment, expand. Organic growth confirms it. 𝕏

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Originally reported by dev.to