Task Success Rate

Task Success Rate is a key metric in usability testing that measures the percentage of users who successfully complete a given task without errors or issues. It helps assess the effectiveness and efficiency of a design by determining how easily users can achieve their goals within a product or system. A high task success rate indicates that the design is intuitive and user-friendly.

Task success rate is a binary metric that doesn't lie — either users completed the task or they didn't. Unlike satisfaction scores that can be influenced by framing, task success in a usability test provides unambiguous evidence of whether your design works. Combining task success rate with time-on-task gives you both effectiveness (did they succeed?) and efficiency (how much effort did it take?) — the two core dimensions of usability.

Microsoft tracks task success rate across their Office products at scale — when they found that users frequently failed to find the 'Track Changes' feature in Word (task success rate under 30%), they added it to the default toolbar and improved its discoverability, resulting in a measurable increase in feature usage and user satisfaction scores.