Viral Coefficient (K-Factor) Calculator

K-factor is invites per user multiplied by the conversion rate of those invites, and a value above 1.0 means each existing user is, on average, bringing in more than one new user through invites alone. That's the mathematical threshold for self-sustaining exponential growth from virality by itself, independent of any paid acquisition or other channel — the calculator flags this as 'is viral' specifically at that cutoff.

Viral cycles is your measurement period divided by the cycle length, rounded down to whole completed cycles. Users after period then sums the geometric series 1 + K + K² + ... + Kⁿ across that many cycles (with a separate formula for the special case K = 1, where the standard geometric formula would divide by zero), so more completed cycles compounds the K-factor's effect further.

The model assumes every viral cycle behaves identically — the same invite rate and conversion rate repeating cycle after cycle for the entire period. Real products rarely sustain that as invite fatigue sets in or the pool of people who haven't already joined shrinks, so a 90-day projection compounds that unrealistic assumption far more times than a 14-day one, making longer periods proportionally less reliable.

No — a K-factor below 1.0 just means invites alone won't sustain exponential growth without other acquisition channels feeding in new users too. The invites you do get still add real users on top of whatever your other channels bring in; the calculator's 'is viral' flag is only measuring whether invites by themselves are enough to grow the user base with zero outside input.