Viral Coefficient

Also called K-Factor and K Factor

How many new users each existing user brings on average, also called the k-factor. Above 1 means self-sustaining, exponential growth from referrals alone.

K-factor = invites sent per user x conversion rate of those invites

Why it matters

A viral coefficient above 1 is rare and powerful, it means growth compounds without paid spend. Even below 1, a higher k-factor lowers your effective acquisition cost, so it is worth engineering into the product.

For example

Each user invites five friends and 20 percent join, a viral coefficient of 1.0, meaning growth can sustain itself without paid spend.

Related terms

Virality Referral Program Network Effects

Go deeper

See how founders actually handle this on Money, pricing and metrics, part of the Starting Up hub.

eChai Partner Brands