Definition
Task Completion Rate measures the usability of a specific flow by tracking what proportion of users who start a task successfully finish it. It is the gold standard UX metric because it directly captures whether the interface enables users to accomplish their goals. Low task completion rates indicate usability friction — confusing layouts, unclear CTAs, validation errors, or broken flows. Track this metric before and after any UX/UI change to quantify impact.
Formula
How to measure
Define the task clearly (start event and completion event). Track `task_start` and `task_complete` events. Calculate completion rate per task. Supplement with session recordings or click heatmaps to understand where and why users drop off. Segment by device, user experience level, and A/B variant.
Industry benchmarks
Well-designed flows: 85–95% completion. Complex multi-step forms: 60–80%. Checkout flows: 65–85% (cart abandonment is the inverse). If any core task falls below 70%, it warrants immediate UX investigation.