What is Viral Coefficient (K-Factor)?
The viral coefficient (K-factor) measures how many new users each existing user generates through referrals, sharing, or network effects.
The viral coefficient (K-factor) measures how many new users each existing user generates through referrals, sharing, or network effects. A K-factor > 1 means viral growth — each user brings more than one new user, creating exponential growth.
Formula: K = (invitations sent per user) × (conversion rate per invitation). If each user invites 5 people and 25% sign up, K = 5 × 0.25 = 1.25.
Viral loops: Inherent virality (the product requires others to use it, like Slack), Collaborative virality (the product is better with others, like Google Docs), Word-of-mouth virality (the product is remarkable enough to talk about, like ChatGPT), and Incentivized virality (users get rewards for referrals, like Dropbox's storage bonuses).
Why It Matters
A viral coefficient > 1 means your user base grows exponentially without proportional marketing spend. Even a K-factor of 0.5 means every 2 users generate 1 additional user — cutting your effective CAC by 33%.
Frequently Asked Questions
What is a good viral coefficient?
K > 1.0 means viral growth (rare). K of 0.3-0.7 is strong organic growth amplification. K < 0.1 means negligible viral effect. Most B2B products are 0.2-0.5.
How do you increase the viral coefficient?
Make the product better with more people (network effects), reduce sharing friction (shareable links, embeds), and make value visible to non-users (e.g., Calendly shows the product to every meeting recipient).
Related Terms
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