NPS vs the PMF survey: which one actually measures product-market fit?

Both metrics are seductive for the same reason: one question, one number, easy to track. So teams reach for the one they already know — usually NPS — and assume it doubles as a read on product-market fit. It doesn't, quite. Here's why, starting with what each one actually asks.

What NPS measures

Net Promoter Score asks one question: "How likely are you to recommend us to a friend or colleague?", on a 0–10 scale. You bucket the answers — Promoters (9–10), Passives (7–8), Detractors (0–6) — and the score is the percentage of Promoters minus the percentage of Detractors. It runs from −100 to +100.

What NPS is genuinely good at: tracking loyalty and advocacy across a large customer base over time. It's a relationship metric. A rising NPS tells you people feel better about you and are more likely to spread the word. That's valuable — it just isn't the same question as "do you have product-market fit?"

What the Sean Ellis survey measures

The Sean Ellis survey asks a different question: "How would you feel if you could no longer use this product?" — very disappointed, somewhat disappointed, or not disappointed. Your score is the percentage who say "very disappointed," and the benchmark for product-market fit is 40%.

This measures dependency, not advocacy. Not "would you say something nice about us," but "would your week get worse without us." That's a higher, more telling bar — and it's the one that maps to product-market fit. More on the 40% rule here.

The core difference: recommendation isn't dependency

Here's the whole thing in one line.

Think about the tools you'd rate a 9 or 10 on NPS — pleasant, well-designed, you'd mention them if a friend asked. Now think about the much shorter list you would be genuinely upset to lose tomorrow. That second list is product-market fit. The gap between those two lists is exactly the gap between NPS and the Sean Ellis score.

Why NPS falls short as a PMF metric

• No PMF threshold. The Sean Ellis test has a validated line — 40%. NPS has rough benchmarks for "good" (loosely, 30+ is solid, 50+ strong), but nothing that says "this is the point of product-market fit." You're left interpreting.
• Advocacy can outrun dependency. People recommend things that are pleasant, cheap, or socially flattering to mention — not only things they rely on. A high NPS can mask a product that's nice-to-have, not must-have.
• It's sensitive to the moment. NPS is easily swayed by a recent support interaction, a price change, or a single bad week — useful for CX, noisy as a fit signal.

Why the Sean Ellis survey is built for PMF

• A real benchmark. 40% is an empirical line Sean Ellis calibrated across roughly 100 startups — the threshold that separated the ones that grew from the ones that stalled.
• A predictive segment. The "very disappointed" group is the cohort that retains and refers. Tracking its size tells you whether your core is growing.
• It hands you the "why." The follow-up questions reveal who loves you and why — your ICP and your roadmap — in the same survey. Here's how to run it.

When to use each

This isn't really NPS or the Sean Ellis survey — they answer different questions, so the smart move is to use each for its job:

• Use the Sean Ellis survey when the question is "do we have product-market fit, and is it improving?" It's your primary fit metric, especially early, and the one to push past 40%.
• Use NPS when the question is "how is our relationship with our customer base trending?" It's a strong ongoing loyalty and customer-experience signal at scale.

If you only have the bandwidth to track one number while you're hunting for product-market fit, make it the Sean Ellis score. NPS is the metric you layer on once you have fit and you're managing a growing base of customers. One tells you whether you've built something people need; the other tells you how they feel about you over time. You want the first answer before you obsess over the second.