Viral Coefficient (K-Factor)
Viral coefficient measures organic user-generated growth through referrals and invitations.
Formula
K = Invitations Per User × Conversion Rate
Interpreting K-Factor
K greater than 1: Viral growth. Each user generates more than one new user, creating exponential growth without marketing spend.
K = 0.5-1.0: Sub-viral but strong. Significant organic growth boost, reduces CAC substantially.
K less than 0.5: Moderate to low virality. Helpful but requires paid acquisition for scale.
Example
Collaboration tool with 1,000 users:
- Each user invites 5 colleagues
- 20% of invites convert to signups
- K = 5 × 0.20 = 1.0 (viral!)
- Cycle 1: 1,000 new users
- Cycle 2: 2,000 new users
- Exponential growth continues...
Viral Cycle Time
K-factor combined with cycle time determines growth speed. K = 0.5 with 2-day cycle beats K = 0.7 with 30-day cycle.