Viral Coefficient Calculator

About this calculator

The viral coefficient — often called the k-factor — measures how many new users each existing user brings in on average, calculated as invites sent per user × invite-to-signup conversion rate. If a user sends 5 invites and 20% convert, k = 1.0.

A k-factor above 1.0 means every user brings in more than one new user on average, so the product can theoretically grow through word-of-mouth alone without any paid acquisition — true viral, compounding growth. A k-factor below 1.0 means the viral loop still helps but can’t sustain growth by itself and needs to be paired with other acquisition channels. Growth marketers and product managers at consumer and B2B products with sharing or referral features — the pattern popularized by early Dropbox and PayPal — calculate this figure to see whether their invite mechanics are actually compounding.