Substack · Metrics · Mid · 45 to 60 minutes

How should Substack measure success?

Substack is a platform where writers publish directly to subscribers and can earn money from paid subscriptions. Answer this product management case and get it graded line by line against a weighted rubric.

Metrics
Product strategy
Tradeoff analysis
Structured communication

The situation

The VP of Product has asked you, a PM on the growth side, to recommend how Substack should measure success across several product teams. Today, teams are leaning toward separate funnel metrics, such as visit to checkout, checkout to paid conversion, retention, and revenue per user. That helps each team focus, but recent experiment reviews have exposed a problem. A change that helps one step can hurt another, and debates often end up with leadership because there is no shared way to judge the net effect. This matters more now because Substack's product strategy depends on a focused experience for writers and readers, not a broad feature set, so local optimization could damage simplicity, subscription quality, or trust. Leadership wants a metric system that speeds decisions, gives teams autonomy, and still reflects company strategy if priorities shift over time. Your job is to recommend the structure, the key metrics, and how teams should use them when results conflict.

What to produce

Write a 1 to 2 page product metrics memo.

Your answer must

Recommend a measurement framework for this product area and explain why it is better than letting each team optimize a separate funnel metric in isolation.
Define the primary metric or metric set precisely, including formula, time window, and why it fits Substack's strategy and business model.
Propose 2 to 4 supporting or guardrail metrics, and state what risk each one protects against.
Show how the framework would evaluate a case where an experiment improves an upstream funnel step but weakens downstream purchase or monetization.
Explain how teams would use the framework day to day, including metric ownership and when the framework should be revisited if strategy changes.

Constraints

Use only information in the prompt plus clearly labeled assumptions.
Do not propose a major change to Substack's product positioning, business model, or target persona.
Your recommendation must work across at least two product teams and reduce the need for routine executive tie breaking.
Keep the system simple enough to use in regular experiment reviews.

Format

Use sections for recommendation, metric definitions, guardrails, tradeoff example, and review process.

How Substack actually played it

Makes the case for one company metric with one controllable metric per team, then uses Substack's own growth to show the idea in practice.

Give each team a metric it can directly move
Use the company metric to set guardrails
Revisit the metric as strategy changes

Built from Do you really need a North Star Metric? by Aakash Gupta.