Metrics come up in almost every PM interview because you cannot make product decisions without knowing what to measure. Interviewers use metrics questions to test analytical thinking — they want to see whether you understand not just what a metric is but why it matters and what decisions it enables. Here is a fluency guide to the metrics that come up most.
DAU/MAU ratio (stickiness)
The DAU/MAU ratio measures stickiness — the percentage of monthly users who return daily. WhatsApp sits around 85%. Most apps land between 10% and 20%. A rising ratio means your product is becoming more essential to users' daily lives; a falling ratio is an early warning signal that engagement is softening even if total user numbers look fine.
Churn rate
Churn is the percentage of users or customers who stop using your product in a given period. Five percent monthly churn means you lose roughly 46% of your users over a year. Churn is the floor through which growth leaks — no acquisition strategy can fix bad retention. When PMs talk about product-market fit, high retention is the most concrete signal they are looking for.
LTV:CAC ratio
LTV is the lifetime value of a customer — how much revenue they generate over their relationship with the product. CAC is the cost to acquire them. A ratio below 1 means you lose money on every customer. A ratio of 3:1 is generally considered healthy for SaaS. A ratio of 5:1 or above often means you are under-investing in growth — you could be spending more on acquisition and still be profitable.
The NPS trap
Net Promoter Score is easy to measure and hard to act on. A score of 40 tells you roughly how many promoters you have versus detractors, but it tells you almost nothing about what to fix. The real value in NPS is in the verbatim responses — the open-ended reasons customers give for their score. Those comments are where the product insights live.
The one metric you should always have ready
In any PM interview for a specific product, be prepared to answer: what is the most important metric for this product, and why? This is not a formula question. It is a reasoning question. A strong answer shows that you understand what success looks like for users and for the business — and that you can connect those two things in a single number. Pick the metric, explain the logic, and acknowledge the tradeoffs. That is what interviewers are testing for.