A progress bar should tell users what has been measured, not just reassure them that something is happening.
Consider a hypothetical photo-processing tool: upload progress is measurable in bytes, but the next step might wait in a queue or take a different amount of time for each image. A bar that reaches 99% and then stalls can turn a useful signal into false precision.
My proposed default would be:
- Use a percentage for work with a meaningful, known total.
- Use explicit stages such as Queued → Processing → Ready when completion time is uncertain.
- Show completed-file counts for batches, while making clear that files may take different amounts of time.
- Keep failure and cancellation states separate from progress.
There is an accessibility detail too: status updates should be available to assistive technology without moving keyboard focus. W3C's guidance on status messages also warns against making updates too chatty; announcing every tick is not necessarily helpful.
Where would you draw the line between a useful estimate and false precision? Would you show stage labels, an estimated range, or a percentage when processing time varies?
Cover: original AI-generated concept illustration of fictional processing interfaces, not a product screenshot or performance result.