Explain how you would build a driver-based model for a subscription business with monthly churn.
A core FP&A interview question — asked in analyst and associate interviews across IB, PE, and the Big 4.
THE SHORT ANSWER
I'd start with the subscriber base: opening subscribers + new subscribers - churned subscribers = closing subscribers. New subscribers are driven by marketing spend and conversion rates. Churn is modeled as a percentage of the opening base. Revenue = subscribers × average revenue per user (ARPU). I'd also model upgrades/downgrades. Costs include variable costs per subscriber and fixed costs. The model rolls forward monthly, allowing sensitivity to churn rate and ARPU changes. This approach ties operational drivers to financial outcomes.
WHAT INTERVIEWERS LISTEN FOR
- ✓Subscriber waterfall: opening + new - churn = closing.
- ✓New subscribers driven by marketing and conversion.
- ✓Churn as a percentage of opening base.
- ✓Revenue = subscribers × ARPU.
COMMON MISTAKES
- ✗Using a flat growth rate instead of driver-based inputs.
- ✗Ignoring churn or modeling it incorrectly.
- ✗Not separating new and existing subscriber revenue.
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