K-factor
How many new users each user brings in.
k = invites per user × share who join
Worked example: 4 × 0.15 = 0.6.
Why it matters
Above 1, each wave of users is bigger than the last. Below 1, each wave shrinks, and the loop fades out.
How to use it
- Measure invites sent per user.
- Measure the share of invites who join.
- Multiply them, and treat anything under 1 as a bonus on top of other growth.
Example
4 invites × 15% joining = 0.6. So 1,000 users bring 600, then 360, then 216, and about 2,500 in total.
Watch out
It says nothing about whether the people who join stay. Forced invites can raise it, and still harm the product.