PM Gym

Understanding Growth Loops

Turn output back into input so growth compounds

A funnel is linear — pour users in the top, some fall out the bottom, and you must keep refilling forever. A growth loop feeds the output of one cycle back in as the input to the next, so the product helps grow itself. This guide covers how loops work, their common types, and why they compound where funnels only leak.

Step-by-step lessons

Think in Loops, Not Just Funnels

Four short lessons: loops vs. funnels, the anatomy of a loop, the three common types, and why loops compound or stall.

1

Loops vs. Funnels

The classic model of growth is a funnel: a one-way path where you pour users in the top and a fraction convert at the bottom. It's linear — to keep growing, you must keep pouring more in. A growth loop is circular: the output of each cycle becomes the input to the next, so growth can feed itself.

Linear

Funnel

One-way. Needs constant external refilling at the top. Asks: "how do we get more in?"

Circular

Growth loop

Output reinvested as new input. Compounds. Asks: "how does each user generate the next?"

Quick check

What's the key structural difference between a funnel and a growth loop?

2

Anatomy of a Loop

Every growth loop has the same skeleton: an input, an action the user takes, an output that action produces, and a step where that output is reinvested as the next input.

A content loop, step by step

Input: a new user arrives. Action: they create a public playlist. Output: that playlist gets shared and indexed by search engines. Reinvest: new listeners discover it, arrive, and some create playlists of their own — which is the input again.

The output (new users) circles back to produce more of the input. That closure is what separates a loop from a one-way funnel.

Quick check

In "user creates content → content gets found in search → new users arrive → some create content," what makes this a loop rather than a funnel?

3

Three Common Loop Types

Most growth loops fall into three families, based on what the reinvested output is: other users, content, or money.

Viral loop

Users bring in other users directly — invites, referrals, or collaboration that exposes non-users to the product.

Content loop

Users (or the product) generate content that attracts new users via search or sharing, some of whom generate more content.

Paid loop

Revenue from users funds acquisition of more users, whose revenue funds more acquisition — only sustainable while a customer earns back more than they cost.

Quick check

A company reinvests subscription revenue into paid ads that acquire more subscribers, whose subscription revenue funds still more ads. Which loop type is this?

4

Why Loops Compound (or Stall)

A loop's health comes down to three things: how fast each turn completes (cycle time), how many new inputs each turn produces (the loop factor), and the friction at each step. Small changes here compound dramatically — in both directions.

Cycle time

How long one full turn of the loop takes. Shorter cycles compound faster.

Loop factor

New inputs produced per cycle. Above 1 and the loop grows; below 1 and it shrinks.

Friction

Drop-off at any step chokes the whole loop; the weakest step caps it.

Loops run in reverse too: if the loop factor drops below 1, decline feeds decline.

Quick check

A viral loop where, over time, each user brings in an average of 0.8 new users. What happens to the loop?

Review the concepts

Growth Loops Flashcards

6 cards covering the essentials. Click a card to flip it.

Foundation Card 1 of 6

Growth Loop

Click to flip

Tip: say the answer out loud before flipping.

Explanation

In practice

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Apply what you learned

Practice Scenarios

15 situations that test whether you can tell a loop from a funnel, identify a loop's type, and diagnose why it compounds or stalls.

Scenario 1

A team's entire growth model is: buy ads → users land → some convert → buy more ads with the marketing budget, sized by a fixed quarterly plan.

Is this a loop or a funnel, and why?

Scenario 2

A design tool grows because users share editable project links with collaborators, who sign up to edit and then share their own projects.

Which loop type is this?

Scenario 3

A blog-style product grows as users publish public posts that rank in search, drawing readers who sign up and publish their own posts.

Which loop type, and what's the reinvestment?

Scenario 4

A viral loop currently has each user bringing in an average of 1.3 new users per cycle.

What does a loop factor of 1.3 imply?

Scenario 5

Two viral loops have the same loop factor of 1.2, but one completes a cycle in 2 days and the other in 30 days.

Which grows faster, and why?

Scenario 6

A PM wants to improve a content loop but every step is roughly equal except publishing, where 90% of users drop off before ever creating a post.

Where's the leverage?

Scenario 7

A subscription business reinvests revenue into ads, but its customer acquisition cost has risen above what an average customer pays over their lifetime.

What's happening to this paid loop?

Scenario 8

A founder describes their growth as a "funnel" and asks only "how do we get more visitors to the top?"

How would loop thinking reframe the question?

Scenario 9

A team adds a referral feature, but users have such a poor first experience that few stay long enough to refer, and those referred also churn fast.

Why isn't the viral loop working?

Scenario 10

A product's growth has quietly reversed: usage and new signups both shrink a little more each month.

How might a loop explain this?

Scenario 11

A PM claims their SEO strategy is automatically a "growth loop" because it brings in users from search.

Is bringing users from search enough to make it a loop?

Scenario 12

A team wants to prioritize between two improvements: one raises the loop factor from 1.1 to 1.3, the other has no effect on the loop.

Which is more strategically valuable for compounding growth?

Scenario 13

A viral loop's invite step works, but invited users land on a confusing signup page and most never activate.

How does this cap the loop?

Scenario 14

Leadership asks why a competitor with a strong content loop keeps pulling ahead despite spending less on ads.

What's the likely explanation?

Scenario 15

A marketplace grows because more buyers attract more sellers, and more sellers (with more selection) attract more buyers.

How should you describe this structure?

Lock it in

Guess the Term

Read the clues and name the concept. The fewer clues you need, the more points you score.

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Keep it handy

Growth Loops Quick Reference

The whole topic on one screen.

Loops vs. Funnels

Funnel

Linear, one-way — needs constant refilling at the top.

Loop

Output reinvested as new input — compounds on its own.

Anatomy of a Loop

1

Input

A new user or action enters.

2

Action

The user does something.

3

Output

That action produces something (users, content, revenue).

4

Reinvest

The output becomes the next input.

Three Loop Types

Viral

Users bring users (invites, referrals, collaboration).

Content

Content attracts users who make more content.

Paid

Revenue funds acquisition — only while LTV > CAC.

Why Loops Compound or Stall

Cycle time

Shorter turns compound faster.

Loop factor

Above 1 grows; below 1 decays.

Friction

The weakest step caps the whole loop.

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