How this growth loop worked
A user signs up, creates a booking link, and drops it into an email or calendar invite. The invitee has no account. They pick a slot and book, using the product as a recipient with no signup required. Some of those invitees later need to schedule their own meetings, so they sign up and send links of their own. Each new sender exposes more non-users, and the output feeds the input.
The loop compounded because distribution was a side effect of normal use. You could not book with the tool without showing it to someone who had never seen it, and that person met the value as a guest before spending anything. At an illustrative K near 0.40, the loop does not sustain itself; it stretches every other channel instead. Each paid or organic signup drags a fraction of a free one behind it, cutting blended acquisition cost.
Bake distribution into the core action instead of bolting a referral program beside it. Calendly never asked anyone to invite a friend; the invite was the job. Design your primary workflow so using it puts the product in front of a non-user who gets value first. Then watch cycle time: a short loop, illustrated here around five days, compounds faster at the same K. A sub-1 loop that lowers CAC is still worth building.