Net dollar retention: Answer Guide 2027
Net dollar retention (NDR) measures how much revenue a cohort of existing customers generates this period versus last — including expansion, contraction, and churn. Above 100% means the customer base grows revenue on its own; below 100% means it shrinks. In a net dollar retention interview, give the formula, the benchmarks, and why SaaS investors obsess over it.
Net Dollar Retention Interview Questions: What They Test
The formula: starting ARR from a customer cohort, plus expansion and upsell, minus contraction and churn, divided by starting ARR. NDR above 120% is generally considered excellent, 100–120% healthy, and below 100% a warning sign — though benchmarks may vary by segment and contract structure.
Interviewers want the "why it matters" story. High NDR means growth compounds without new customer acquisition — the business grows even with zero new logos, which is why best-in-class SaaS companies command premium multiples. It also reveals product-market fit: customers who expand are voting with their wallets.
How to Answer a Net Dollar Retention Interview Question
- State the formula. "NDR = (starting ARR + expansion − contraction − churn) / starting ARR, measured on the same customer cohort."
- Interpret the bands. "Above 120% is elite, 100–120% healthy, below 100% means the base is leaking — benchmarks may vary."
- Explain the compounding. "At 120% NDR, revenue grows 20% with zero new customers — that is the magic investors pay for."
- Distinguish gross retention. "Gross retention excludes expansion, so it caps at 100% — NDR includes it, which is why NDR can exceed 100%."
Common Mistakes in Net Dollar Retention Interview Answers
- Confusing NDR with gross retention. Gross retention measures churn only; NDR adds expansion — mixing them up is the classic error.
- Using different cohorts. NDR must be measured on the same starting customer set — adding new logos inflates it.
- Ignoring the segment mix. Enterprise and SMB cohorts have very different NDR norms — always segment before judging.
NDR is arguably the single most important SaaS metric in interviews — formula, benchmarks, and the compounding story, in that order.
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FAQ
Q: What is the difference between NDR and gross revenue retention? A: Gross retention counts only contraction and churn (capped at 100%); NDR also includes expansion and upsell, so it can exceed 100%.
Q: What is a good net dollar retention rate? A: Above 120% is generally considered world-class, 100–120% healthy, and below 100% concerning — with variation by segment.
Q: Can NDR exceed 100% without new customers? A: Yes — that is exactly what it measures: whether the existing customer base expands spending faster than it churns.
Q: Why do investors prize high NDR? A: Because it means efficient, compounding growth — revenue grows without proportional sales and marketing spend on new acquisition.
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