Viral Coefficient Calculator
Work out your K-factor from invites per user and their conversion rate, and see whether each user brings in more than one new user — the threshold for true viral growth.
How it works
K = invites per user × invite conversion rate · New users = existing users × K · If K < 1, total = users ÷ (1 − K)
The viral coefficient K is how many new users the average user recruits: invitations sent times the share of those invitations that convert. When K is 1 or more each cohort more than replaces itself and growth becomes self-sustaining and exponential. When K is below 1 — the usual case — virality still helps by amplifying every other acquisition channel by a factor of 1 ÷ (1 − K), but it cannot carry growth on its own.
Worked example
If each user sends 8 invitations and 12% accept, K = 8 × 0.12 = 0.96. That is just under 1, so 1,000 users spawn 960 more this cycle, and the amplification factor is 1 ÷ (1 − 0.96) = 25× over all cycles.
Frequently asked questions
What does a viral coefficient above 1 mean?
Each existing user brings in more than one new user, so the base grows by itself without paid acquisition — true viral, exponential growth. Sustaining K above 1 for long is rare and powerful.
Is a K below 1 useless?
Not at all. A K of 0.5 still multiplies every other channel by 1 ÷ (1 − 0.5) = 2×, effectively doubling the reach of your paid and organic acquisition. Most successful products live below 1.
What else affects viral growth besides K?
Cycle time — how fast invites turn into new users — matters as much as K. A high coefficient with a slow loop grows slowly; a modest coefficient with a fast loop can outpace it.
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Educational estimate, not financial advice.