Is your invite mechanic actually viral, or just helpful?
K ≥ 1 means each user brings in more than one new user on average — genuine, self-sustaining growth. Below that, invites still help, they just don't compound on their own.
Your numbers
The base you're projecting growth from.
Average across all users in a cycle, not just active inviters.
Share of invites that become new signups.
One cycle is however long it takes a new user to start inviting others.
Viral coefficient (K)
0.36
Each existing user brings in 0.36 new users on average per cycle.
Users after 4 cycles
3,421
From 1,000 starting users.
New users from virality
+2,421
Growth attributable to invites alone, no other acquisition.
K of 0.36 is a real viral-assist effect — invites meaningfully extend your reach, but they won't sustain growth alone. Treat this as a multiplier on paid or organic acquisition, not a replacement for it.
K-factor compounds fastest when cycle time is short — the same K produces very different real-world growth if a cycle takes a day versus a quarter. Pair this with your actual invite-to-active-use timeline before treating the projection as a forecast.
Calculated in your browser — nothing is sent anywhere, and nothing is stored.
The maths, so it isn't a black box.
It multiplies invites by conversion
K equals average invites sent per existing user multiplied by the share of those invites that convert into new signups — the standard viral-coefficient formula, with no hidden adjustments.
Then projects it forward
Applies K compounding across however many cycles you set, the same way interest compounds — showing not just today's K but what it actually does to your user count over time.
And tells you which regime you're in
K at or above 1 is true virality; roughly 0.3 to 1 is a real but partial viral-assist effect; below that, invites are a minor contributor. The threshold changes what you should expect the mechanic to do for you.
Questions about this calculation
However long it typically takes a new user to become active enough to start inviting others themselves — often a week for consumer social products, longer for B2B tools. Use your own product's actual activation-to-invite timeline, not a generic default.
Terms used here
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Where we do this work
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