K-Factor (Virality)

K-Factor is the number of new users each existing user generates through invites, equal to invites sent per user times the conversion rate of those invites.

You multiply the average invites a user sends by the share of those invites that turn into new active users. A K of 0.4 means every 10 users bring 4 more, which decays and stops; a K above 1 means each user brings more than one, and the loop compounds on its own. Most real apps live well below 1 and use virality to lower blended acquisition cost, not to replace paid entirely.

Say each user sends 5 invites and 8 percent of invited people install and activate. K is 5 times 0.08, which is 0.4. Sustained genuine virality above 1 is rare and usually short-lived before saturation pulls it back down.

K-factor without cycle time tells you nothing about speed. A K of 0.6 with a one-day invite loop grows far faster than the same K on a monthly loop, because what matters is K compounded over how often the loop turns. Report the viral cycle time alongside K, and strip out incentive-gamed invites that convert but never stick.

K sets the ceiling; cycle time sets the pace.