Dropbox · Metrics · Mid · 45 to 60 minutes

How Much Should Dropbox Bet on Referrals?

Dropbox is a cloud storage and file sharing service that lets people save, sync, and share files across devices. Answer this product management case and get it graded line by line against a weighted rubric.

Estimation
Metric decomposition
Assumption setting
Strategic judgment
Communication

The situation

The VP of Growth asks you, a PM on Dropbox's self serve acquisition team, for a quick decision memo before the next planning cycle. Dropbox already benefits from natural word of mouth because people invite others to shared folders and links, but leadership is considering whether a more deliberate refer a friend program deserves scarce product and engineering time. Assume Dropbox has about 100,000 registered users today, leadership wants to understand whether referral could be a major contributor on the path to 4,000,000 users over the next 15 months, and recent snapshots suggest referrals might account for roughly 35% of daily signups if the program is working well. The company can only fund a limited amount of growth work next quarter, so every week spent on referral mechanics is a week not spent on core sharing or onboarding improvements. Data is incomplete, and you do not have time for a full experiment before the planning decision. Your job is to size the likely contribution of referral, show how much growth must still come from other sources, and recommend how aggressively Dropbox should prioritize referral work right now.

What to produce

A 1 page decision memo, 500 to 700 words.

Your answer must

State your assumptions clearly, including the growth shape you use and any simplifications about referral performance over time.
Calculate the monthly registered user growth rate needed to move from 100,000 to 4,000,000 users in 15 months.
Estimate the monthly growth attributable to referral if referrals represent 35% of daily signups, and show the math.
Include at least one cross check or sensitivity analysis that tests whether your estimate is reasonable.
Make a recommendation on how much to prioritize referral optimization next quarter, including what growth must still come from non referral sources.
Name 2 to 3 follow up metrics or instrumentation changes you would use to validate the decision after launch.

Constraints

Use only the information in the prompt and back of the envelope math, no outside benchmarks or research.
Do not assume referral is the sole driver of growth, Dropbox also has organic sharing, word of mouth, and media attention.
You cannot wait for a long experiment or a full data warehouse rebuild before making the recommendation.

Format

Use sections titled Assumptions, Sizing, Cross check, Recommendation, and Follow up metrics.

How Dropbox actually played it

Estimates how much of Dropbox's early growth came from its referral program using stated assumptions and simple growth maths. It is a good example of sizing a channel from public numbers.

State your assumptions when you size a channel
Cross check an estimate against other figures
Referral can add a steady share of growth, not all of it

Built from 3900% Growth: Dropbox Customer Referral Program by the Numbers by SaaSquatch.