How does a dynamic segment work?
You write a condition — "started a trial in the last 14 days AND has not sent an invite" — and the platform evaluates it against every person's attributes and event history. When someone crosses the threshold, they enter the segment; when the condition stops holding, they leave. Nobody adds or removes them by hand. This is why a dynamic segment is only as accurate as the tracking plan behind it: if the invite_sent event is never recorded, the segment can never react to it.
Dynamic segment vs static segment
| Property | Dynamic segment | Static segment |
|---|---|---|
| Membership | Recomputed automatically from rules | Fixed until edited by hand |
| Best for | Behavioral targeting that must stay current | A frozen audience — a launch list, a one-off export |
| Risk | A member can exit mid-journey if they stop matching | Goes stale; no new matching users are added |
Why it matters for a two-person team
A dynamic segment is the closest thing a small team has to an extra pair of hands: define "trial ending in 3 days, no payment method" once, and it stays correct forever without anyone maintaining a spreadsheet. It also keeps messaging honest — a churned user drops out of the active-user segment the moment they churn, so they stop receiving upgrade nudges. The full mechanics of building conditions, choosing traits, and avoiding overlap live in the guide to customer segmentation basics; segments also map naturally onto each lifecycle stage you want to message.
What makes a dynamic segment misfire?
Two failure modes dominate. First, membership churn: if a rule sits on the edge of a fast-changing value, people flicker in and out and may receive a journey's first email but never its second — add a stabilising condition or a minimum dwell time. Second, a segment is not a cohort: a cohort freezes its members by a shared start date and tracks them over time, while a dynamic segment reflects only who matches right now. Use a segment to decide who gets a message, and a cohort to measure how a group behaves as it ages.