What is product-market fit — and how do you know when you have it?
Product-market fit (PMF) is the point at which your product satisfies a strong, real demand in a specific market. Marc Andreessen, who coined the term, described it simply: "being in a good market with a product that can satisfy that market."
Before PMF, everything feels hard. After PMF, growth becomes pull-based — customers find you, refer others, and demand more. The distinction between before and after is stark enough that most founders say they "knew it when they felt it."
The Sean Ellis test — the most practical PMF measure
Sean Ellis developed a survey question used by hundreds of successful startups: "How would you feel if you could no longer use this product?" with three answer choices: Very disappointed, Somewhat disappointed, Not disappointed.
The benchmark: if 40% or more of your users answer "very disappointed," you have strong PMF signal. Below 40% means there's still work to do. This test is valuable because it forces users to imagine loss — loss aversion reveals true product attachment in a way that "would you recommend this?" does not.
Other PMF signals to watch
- Organic word of mouth — customers you didn't acquire are signing up because someone told them about you
- Net Promoter Score above 50 — consistently across a meaningful sample size
- Support tickets changing character — from "how do I use this?" to "can you add this feature?" means users are already relying on it
- Churn dropping without intervention — users who started leaving are staying, unprompted
- Sales getting easier — your close rate improves without you changing your pitch
What PMF feels like — in Paul Graham's words
Paul Graham described it as something you can feel: "You can always feel product-market fit when it's happening. The customers are buying the product just as fast as you can make it… Money from customers is piling up in your company checking account."
Conversely, the absence of PMF is also something you can feel — every sale is a struggle, retention is weak, and the product always needs "one more feature" before customers will truly commit.
PMF is not permanent
Markets shift. Competitors emerge. Technology changes customer expectations. A product that had strong PMF in 2020 may not have it in 2026. Successful companies re-validate continuously — especially at major inflection points like entering new markets, changing pricing, or launching new product lines.
Re-run the Sean Ellis test every 6 months. Watch for NPS drift. PMF maintenance is just as important as achieving it in the first place.