Viral coefficient
Viral coefficient is the measure of how many additional users each user brings into a product through referrals; in growth-marketing practice it is used interchangeably with K-factor.
How it is calculated
The viral coefficient multiplies the share of users who refer by the average number of successful signups each referrer produces — the same calculation as K-factor. A coefficient of 1.0 marks the line between a list that needs constant traffic and one that grows on its own.
Why it matters
It is the single number that predicts whether referral loops will carry growth or merely supplement paid and organic traffic. Tracking it over time tells you whether changes to your referral incentives are actually working, rather than guessing from raw signup counts.
Related terms
- K-factor — K-factor is the average number of new signups each existing user brings in through referrals, calculated as the share of...
- Viral loop — A viral loop is a closed cycle where each new user produces actions — most often via referral links, shared invites, or...
For how viral loops drive this number, see the complete guide to viral loops.
Frequently asked questions
- Is viral coefficient the same as K-factor?
- Yes. In everyday growth-marketing usage they refer to the same metric — the number of new users each existing user generates through referrals. Some teams reserve "viral coefficient" for the theoretical figure and "K-factor" for the measured one, but the calculation is identical.
- What viral coefficient is realistic for a SaaS waitlist?
- Most SaaS pre-launch waitlists land between 0.2 and 0.7. Reaching a self-sustaining 1.0+ usually requires a genuinely shareable product and strong built-in mechanics like queue jumping and milestone rewards, not just a "refer a friend" link.
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