Viral Coefficient Calculator
The viral coefficient — invitations times conversion rate — and what it does to growth above and below 1.
K = invites per user × conversion rate of those invites.
How the viral coefficient calculator works
K = invites per user × conversion rate of those invites. Above 1 each user brings more than one new user and growth compounds without paid acquisition; below 1 the loop amplifies other channels but cannot sustain growth alone.
The cycle time matters as much as K. A K of 1.2 with a two-week cycle grows far faster than the same K on a three-month cycle, and most products never exceed K = 1 for long.
Formula: K = invites × conversion rate; amplification = 1/(1−K)
Worked examples
| Inputs | Viral coefficient (K) | Note |
|---|---|---|
| 5 invites at 15% | 0.75 | K = 0.75 — sub-viral but a strong amplifier |
| Above one | 1.25 | K = 1.25 — compounding growth |
| A weak loop | 0.1 | K = 0.1 |
FAQFrequently asked questions
What is the viral coefficient?
K — the number of new users each existing user brings. Invites sent multiplied by the rate at which they convert.
What does K above 1 mean?
Each user brings more than one new user, so the base grows without any paid acquisition. Very few products sustain it for long.
Is K below 1 worthless?
Far from it. K = 0.75 multiplies every other channel by four. A referral loop that is not self-sustaining can still transform unit economics.
Why does cycle time matter?
Because K describes growth per cycle. The same K compounds far faster on a two-week loop than a three-month one.
Why do viral loops decay?
Because the addressable network saturates. Early users have many uninvited contacts; later ones do not.
Where these figures come from
- Interactive Advertising Bureau — measurement guidelines — the impression and viewability definitions CPM depends on
- US Federal Trade Commission — the US advertizing regulator
Last checked: September 2026. These are standard industry definitions; where platforms disagree, the page says so.