Viral Coefficient (K-Factor)
A metric that measures how many new users each existing user brings to your product through referrals.
Definition
The viral coefficient (also called K-factor) quantifies the viral growth of a product by measuring how many new users are acquired through referrals from existing users. A coefficient greater than 1 indicates exponential growth, while less than 1 means growth will eventually plateau.
How to Calculate
Formula:
Viral Coefficient = Invitations Sent Per User × Conversion Rate
Alternative Formula:
K = (New Users from Referrals) ÷ (Total Existing Users)
Real-World Example
Calculation:
- • Each user sends 5 invitations
- • 20% of invitations convert to sign-ups
- • Viral Coefficient = 5 × 0.20 = 1.0
A coefficient of 1.0 means each user brings exactly one new user, maintaining steady growth.
Interpretation
K > 1: Exponential viral growth - each user brings more than one new user
K = 1: Sustained growth - each user brings exactly one new user
K < 1: Declining growth - viral effect alone won't sustain growth