K-factor (viral coefficient)
Virality metric. Do they bring other users?
What is the K-factor (viral coefficient)?
The k-factor, or viral coefficient, is the number of new users each existing user brings in through invites or shares.
Viral loop: the cycle of a user joining, inviting others, and those users inviting more.
How to calculate K-factor
K = Invites sent per user × Invite conversion rate- Invites sent per user
- invites or shares sent in the period ÷ users who could send them
- Invite conversion rate
- new users from invites ÷ invites sent
Where definitions differ
| Variant | Formula | When to use it |
|---|---|---|
| Invite k-factor | Invites per user × Conversion | Measurable when invites are tracked links or codes. |
| Viral cycle time | Average days from a user joining to their invitees joining | A shorter cycle compounds faster at the same k. |
| Word of mouth | Untracked recommendations | Real but not measurable this way; it shows up as organic installs. |
K-factor calculator
Example inputs: change them to your own numbers. The examples only make the calculator show a worked answer; they are not benchmarks or targets. Runs in your browser; nothing you type is sent anywhere.
- Invites per user
- 1.5
- Invite conversion
- 8%
- K-factor
- 0.12
What does a k-factor above 1 mean?
Each user brings in more than one new user, so growth compounds without paid spend for as long as it lasts. Below 1, invites do not sustain growth on their own but still lower the blended cost of acquisition.
How K-factor differs by vertical
| EdTech | Study groups and referral discounts drive invites. |
|---|---|
| Fintech | Referral rewards are common and tracked; watch for reward abuse. |
| OTT and streaming | Shared links to titles act as invites. |
| Gaming | Gifting and team play create invite loops. |
Common mistakes
- Counting invitees who would have installed anyway as viral growth.
- Ignoring cycle time when comparing k-factors.
Questions
How do you calculate k-factor?
Multiply the average invites sent per user by the share of invites that turn into new users. 1.5 invites per user at 8% conversion is a k-factor of 0.12.
Is k-factor the same as viral coefficient?
Yes, the two names are used for the same measure.
How do you track invites in an app?
Give each invite a unique link or code so the new install can be credited to the inviter. Untracked shares cannot be counted in the k-factor.
Why do tools report different values for the same metric?
Because definitions differ: what counts as active, which attribution window applies, whether organic users are included and how days are cut by timezone. Align the definition before comparing numbers.
Which currency do the calculators use?
The calculators show US dollars, but every formula works in any currency: enter your own figures in the currency you report in and read the results in that currency.
What is the difference between a metric and a KPI?
A metric is any measured quantity; a KPI is a metric a team has chosen as a target for judging performance. Most metrics here become KPIs only for the teams whose work moves them.