Value Metric
Error Rate
Error Rate is how often users make mistakes while attempting a task, relative to the opportunities to err.
What is Error Rate?
Error Rate measures how frequently users make mistakes — wrong entries, misclicks, failed submissions — while using your product. It can be expressed per task, per attempt, or against the number of opportunities for error, and it is a core usability and quality signal.
Errors matter beyond the immediate failure: they slow users down, erode confidence, and often precede abandonment. Distinguishing slips (accidental) from mistakes (misunderstandings) points to different fixes.
How to calculate it
Error Rate = Number of Errors ÷ Number of Opportunities for Error × 100
- Number of Errors
- Errors observed during the task
- Opportunities for Error
- Total chances to make an error (attempts or steps)
Worked example
If users make 30 errors across 300 opportunities, error rate = 30 ÷ 300 × 100 = 10%.
What good looks like
- Lower is betterTrend toward zero
The right target depends on the task’s stakes — a payment form should approach zero errors, while a low-risk exploratory task can tolerate more.
Why it matters
Errors are friction made visible. They lengthen tasks, damage trust, and cause drop-off, and on critical flows (checkout, data entry) they translate directly into lost revenue or bad data. Tracking error rate — and the types of errors — shows where the design is fighting the user and where forgiveness (validation, undo, clear recovery) is most needed.
How to improve Error Rate
Prevent errors by design
Use constraints, sensible defaults, inline validation, and clear affordances so mistakes are harder to make.
Make recovery easy
When errors happen, provide clear messages and simple ways to undo or correct, so a slip does not become abandonment.
Frequently asked questions
What is the difference between slips and mistakes?
A slip is an accidental error where the user intended the right action but executed it wrong (a mistyped field). A mistake is an error of intention caused by a misunderstanding. Slips are fixed with better affordances and forgiveness; mistakes are fixed with clearer information and mental-model alignment.
What is a good error rate?
It depends on the stakes of the task. High-consequence flows like payments or data entry should approach a zero error rate, while low-risk, exploratory interactions can tolerate more. Track the rate and the error types over time and prioritize the costliest errors.