Question 1

What is Product-Market Fit (PMF)?

Accepted Answer

Product-Market Fit is when your product satisfies a strong market demand. It means you've built something people want enough to pay for, use regularly, and recommend to others. Marc Andreessen described it as 'being in a good market with a product that can satisfy that market.' You know you have PMF when growth becomes easier and retention improves.

Question 2

What is the 40% rule for PMF?

Accepted Answer

The 40% rule, created by Sean Ellis, states that if at least 40% of your users would be 'very disappointed' if your product disappeared, you've likely achieved Product-Market Fit. This is measured by surveying users with the question: 'How would you feel if you could no longer use [product]?' Responses: Very disappointed, Somewhat disappointed, or Not disappointed.

Question 3

How many survey responses do I need?

Accepted Answer

You need at least 40 responses for the 40% rule to be statistically meaningful, according to Sean Ellis. However, the more responses you get, the more reliable your PMF score. Aim for 100+ responses if possible. Only survey users who have experienced your core value proposition—at least two weeks of active use for most SaaS products.

Question 4

What if I'm below 40%?

Accepted Answer

If you're below 40%, don't panic—most products start there. This is valuable feedback telling you to iterate. Focus on: talking to the users who WOULD be disappointed (your early adopters), understanding why others aren't disappointed enough, improving your core value proposition, and re-surveying after major improvements. PMF is earned, not declared.

Product-Market Fit Calculator

Build what users actually want

Frequently Asked Questions

Related Tools

User Activation Calculator

CAC Calculator

LTV Calculator