Task Completion Rate

Task Completion Rate is a usability metric that measures the percentage of users who successfully complete a predefined task, such as purchasing a product or filling out a form. This metric is crucial for evaluating the effectiveness and efficiency of a product, as a high task completion rate indicates that the design is intuitive and users can easily achieve their goals.

Task completion rate is the most direct measure of whether your product works — not whether it looks good, not whether users like the idea, but whether they can actually do the thing they came to do. For usability testing, it's the first metric to look at before anything else. A product with 60% task completion on its core use case has a fundamental problem; one with 95% has earned the right to focus on delight and optimization.

When Duolingo redesigned their lesson completion flow, they tracked task completion rate as the primary metric — specifically the percentage of users who finished a lesson they started. Each iteration that improved this metric (reducing session length, adding progress feedback, improving mobile tap targets) directly improved their day-2 retention curve.