Viral coefficient

I * CR = K

I = Invitations
CR = conversion rate of invitations
K = viral coefficient

For “viral growth”, we need a viral coefficient greater than 1.

You’ll sometimes hear people call the viral coefficient the K-factor.

Built into the product

Viral growth cannot be executed by a marketing department that can’t code. It has to be built into the product by developers. We want outcomes like:

• Active, happy users invite many new users
• Active, happy users share lots of our app’s content
• Active, happy users use the app longer

To get a viral coefficient of 1 or better, we might need numbers as good as:

• 10% of users to invite their friends
• 10 invitations per user
• 10 content shares per user
• 10% of users active every day
• 10 repeat visits per user every month
• 10% of invitations to be accepted

That should sound hard. To achieve those numbers, we might want to use these techniques:

• Single-step invite flows
• Encourage users to invite friends or share content only at times when user is happiest or really wants to take another action (“To see this video, invite 3 friends.”).
• Address book importers
• User-to-user messaging
• Collaborative filtering for content recommendations

Those are things that developers have to implement, not traditional marketers. Great copy and calls to action are still important, but the viral mechanisms have become engineering tasks.