Offer a generous free tier where the output the user creates carries a small brand mark — 'sent from X' or 'created with X'. Free users become a distribution layer in exchange for the free product.

1. 1

   Pick a reward that's emotionally meaningful but financially sustainable (extension > cash > swag for SaaS).

2. 2

   Make sharing one-tap with pre-filled message and trackable link — friction kills the loop.

3. 3

   Reward both sides — the referrer AND referee — to remove the awkwardness of asking.

4. 4

   Surface the program at the activation moment, not on the homepage — happy users refer; lukewarm users don't.

5. 5

   Measure K-factor weekly: invites sent × accept rate. <0.3 is broken; >1.0 is the dream.

6. 6

   Cap reward stacking to prevent gaming, but don't make legitimate referrers feel watched.

Linktree built a $1.3B business primarily on this mechanic — every free user's link-in-bio page included a small "Make your own Linktree" badge, turning every Instagram bio in their user base into a public ad. They reached 24M users at a near-zero CAC.

• ✗Calling the test too early — read results at full 7-day multiples to neutralize day-of-week effects.
• ✗Skipping the audience / segment definition — broad targeting dilutes the signal and inflates CAC.
• ✗Failing to instrument the downstream metric — clicks are not revenue.
• ✗Watch-out from the playbook: Make the branded mark genuinely small and clean — heavy-handed branding triggers paid upgrades but also kills the free distribution loop.

Tools producing publicly-shared output (forms, signatures, docs)