Task success rate: the simplest navigation measure

Key takeaways

Task success rate is the share of participants who complete a task, such as finding a price, in a usability test. It is the simplest and most telling navigation measure: if people cannot find something, little else matters. Define success clearly before the test, score partial success consistently and compare rates before and after changes.

• Task success rate is completed tasks divided by attempts.
• Define what counts as success before testing.
• Score partial success consistently, or not at all.
• Compare rates for the same tasks before and after changes.

What is task success rate?

Task success rate, also called completion rate, is the percentage of attempts in which a participant achieves a defined goal on a website, such as reaching the correct service page. If eight of ten attempts to find the price succeed, the rate is 80%. It is a core measure in usability testing.

• How clear website navigation improves user experience
• Navigation usability testing: five tasks, five people

How do you measure it?

Run a usability test with realistic tasks and a clear end point for each. Mark each attempt as success or failure, then divide successes by attempts. Use the same tasks each time you test, so results are comparable.

• Write tasks with a clear end point.
• Define success, such as reaching the right page.
• Mark each attempt success, partial or failure.
• Calculate successes divided by attempts.
• Repeat the same tasks after changes.

How should partial success be scored?

Decide before the test. A common approach is to count partial success, such as reaching the right section but not the right page, as half. Some teams prefer only full success. Either is fine if you apply it the same way every time.

What is a good success rate?

For the core tasks on a business site, such as finding a service, a price or contact details, aim for nearly everyone to succeed. A rate below about 80% on a core task is a strong sign of a navigation problem. These are GBL's working thresholds rather than an industry standard; with five participants, treat rates as indicative.

Why not rely on analytics instead?

Analytics show where visitors went, but not what they were trying to do, so you cannot tell success from failure. A visitor who reaches the contact page may have found it easily or after five wrong turns. Task success needs a known goal, which only testing provides. Use both together.

• Navigation metrics: proof visitors find their way
• GA4 path exploration: see the routes visitors really take

What does this look like in practice?

A pattern we see: in a test with five people, all five find the contact page, four find a service, but only two find the price list. Renaming and moving the price link, then testing with five more, gives a clear before and after on the same task.

• See client work
• Website Design & Development for UK businesses

Task success checklist

• Write core tasks with clear end points.
• Define success and partial success.
• Score every attempt.
• Flag tasks below about 80%.
• Retest the same tasks after changes.

• Time on task: how long it takes to find what matters
• System Usability Scale: a 10-question score for your site

Next step

List your five core tasks and write the end point that counts as success for each.