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TTFB (Time to First Behavior)

By Jason Hreha
  • 1 min read
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Time to First Behavior (TTFB) is the elapsed time from a defined start event, such as first exposure, to the predefined first beneficial completion of the target behavior. It shows how quickly the solution enables the validated behavior.

Key Insight

A long TTFB can point to friction or to a solution that does not yet enable the behavior. Whether a shorter TTFB predicts later behavior retention is a hypothesis to test in each product and cohort. No general effect size is established. BS-0002

Measurement 

TTFB = timestamp(first_behavior_completion) - timestamp(first_exposure)

First exposure is typically defined as:

  • App install or first open
  • Account creation
  • Landing page arrival
  • Onboarding start

First beneficial completion is the first completion of the validated target behavior that meets the predefined criteria. It is not a proxy action.

Examples

These are examples, not measurements from real companies.

Product type Start event First beneficial completion
Photo-sharing app First open First photo posted to an intended audience
Language-learning app First open First lesson completed
Team messaging tool Workspace created First message that receives a reply
Brokerage app Account approved First order placed

Set a target from the behavior’s required timing and domain evidence. Targets such as under 5 minutes for a consumer flow or under 1 day for a B2B pilot are starting points, not benchmarks. See Measurement Standards.

Why TTFB Matters

  1. Validates Solution Fit: If TTFB is long, the solution may not be enabling the behavior effectively
  2. Tests a Retention Hypothesis: Compare TTFB with later behavior retention in your own cohorts before you treat it as a leading indicator
  3. Identifies Friction: A high median TTFB can point to onboarding or UX barriers
  4. Segments Users: TTFB distribution can identify distinct user segments with different needs

Optimization Strategies

  • Remove friction: Reduce steps between exposure and behavior
  • Progressive disclosure: Show only what’s needed to perform the first behavior
  • Default to action: Pre-populate or pre-select to enable faster completion
  • Immediate feedback: Reward the first behavior to reinforce continuation

Relationship to Other Metrics

Metric Relationship
Δ-B (Delta-B) TTFB describes the first completion. Δ-B measures the change in the target behavior rate after an intervention
bPMF TTFB describes the first completion. bPMF describes repeat completion at a threshold frequency within a cohort window
Retention Test whether faster TTFB predicts behavior retention in your cohorts. No general relationship is established

See also