Viral Coefficient (K-Factor)
A measure of how many new users each existing user generates through referrals and sharing.
What it means
The viral coefficient (K-factor) quantifies word-of-mouth growth. If K = 1.5, every user brings in 1.5 new users on average. A K-factor above 1 means exponential growth - each user generates more than one additional user. Even a K-factor below 1 is valuable, as it reduces your effective CAC by supplementing paid acquisition with organic referrals.
Formula
K = Number of invites per user × Conversion rate of invites
Why it matters
A K-factor above 1 is the holy grail of growth - it means your user base grows exponentially without additional marketing spend. Even a K of 0.5 means referrals provide half your growth for free. Building referability into your product and content is one of the highest-leverage activities for any founder.
What is viral coefficient?
The viral coefficient (K-factor) measures how many new users each existing user brings in through referrals and sharing. A K above 1 means exponential, self-sustaining growth.
How do you increase viral coefficient?
Make sharing easy and rewarding, build network effects into your product, create share-worthy content, add referral programs, and make your product visible in users' workflows.
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