Product-market fit (PMF) is the single most important milestone for an early-stage startup. It’s when your product is pulled by the market faster than your sales team can push it. Before PMF, growth is expensive and fragile; after PMF, it becomes a question of scaling what works.

Marc Andreessen’s original definition (2007)

“Product-market fit means being in a good market with a product that can satisfy that market.”

Indicators Andreessen listed:

• Customers are buying the product as fast as you can make it.
• Usage is growing exponentially.
• You’re hiring sales and customer support as fast as you can.
• Press is reaching out to you.

How to measure PMF

1. Retention curves (the gold standard)

Plot the percentage of each weekly or monthly cohort still using the product over time.

• Flattening retention curve: Likely PMF.
• Continuously declining curve: Not yet PMF.
• Smile curve (users return after initial drop-off): Classic PMF signal.

2. Sean Ellis test

Survey active users: “How would you feel if you could no longer use this product?”

• Very disappointed.
• Somewhat disappointed.
• Not disappointed.

If ≥40% say “very disappointed,” you likely have PMF in at least one segment.

3. Organic growth

• Share of new customers coming from referrals or word of mouth.
• K-factor: Average number of new users each existing user brings in.

4. Net Revenue Retention

• NRR > 120% in B2B strongly correlates with PMF.
• NPS > 50 in consumer strongly correlates with PMF.

Types of PMF

1. Early PMF: 20–100 customers who love you.
2. Product-channel fit: Product that matches a repeatable acquisition channel.
3. Model-market fit: Pricing and monetization align with buyer willingness.
4. Category leadership: PMF across a broad segment, not just a niche.

Common false signals

• Pilot PMF: 5 customers who signed pilots but haven’t renewed.
• Founder-driven sales: Every customer closed by the founder personally.
• Discount-driven retention: Retention propped up by heavy discounting.
• Vanity usage: High engagement with low revenue attach.

PMF sector differences

• B2B SaaS: 3+ expansion customers, above 100% NRR, payback under 24 months.
• Consumer: High DAU/MAU ratio, viral growth, low paid CAC.
• Marketplace: Liquidity on both sides; transaction growth.
• Dev tools: High voluntary adoption and organic GitHub/Discord engagement.

Practical takeaway

1. Founders: Don’t scale GTM until PMF is measurable — you’ll burn cash.
2. Investors: Pressure-test PMF by cohort data, not narrative.
3. Operators: Run the Sean Ellis test quarterly; PMF can decay.

Further reading

• Sean Ellis PMF Test: https://pmfsurvey.com/
• First Round Review on retention: https://review.firstround.com/