Product-Market Fit Calculator
Ask users how they'd feel if they could no longer use your product, then enter the counts. The threshold is 40% answering "very disappointed" — but at the sample sizes most founders have, the interval around that number matters more than the number.
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4 more "very disappointed" answers would reach 40%.
Only survey people who have actually used the product recently. Sean Ellis’s own qualifier was at least twice in the last two weeks — a score computed over unengaged signups means nothing.
How the score works
PMF score = very disappointed ÷ total responses × 100. The convention, from Sean Ellis's work across roughly 100 startups, is that 40% or above indicates product-market fit.
The confidence interval is p ± 1.96√(p(1−p)/n). At 30 responses and a 40% score, the interval runs from roughly 22% to 58% — which is why this tool flags samples under 40 as underpowered.
Survey only people who have used the product recently. Ellis's own qualifier was at least twice in the past two weeks; a score computed over dormant signups measures nothing.
Questions people ask
Why 40%?
It's an empirical benchmark from surveying around 100 startups, not a mathematical law. Treat it as a useful line rather than a precise threshold — 38% with a strong upward trend is more encouraging than a static 41%.
How many responses do I need?
At least 40 for the interval to be informative, and 100 or more before making a decision on it. Below 40 the tool will say so.
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