I have a project with different tasks.
Someone fills the column “% Complete” to reflect the work that it’s been done.
Sometimes those task are late and sometimes are ahead in time.
what I would like to know is where I should be (%-wise) for each task and summarise that for the whole project (summary task)
Percent complete doesn’t always translate to progress-in-time in Microsoft Project, especially as it relates to summary tasks. Depending on how work is scheduled and how resources are assigned/loaded, the percent complete value can look very skewed if treated as a day-for-day progress indicator. Of course, when things are skewed to look ahead of schedule, no one complains, but when you appear to behind schedule, you probably have to answer some difficult questions.
We had a similar thread on our support forum about a year ago, which I am including for your reference.
This may help provide some clarity on why percent complete looks off on summary tasks, and how to remedy it somewhat in your data.
For presentation purposes (e.g. with OnePager Pro) there are graphical ways to overcome the discrepancy. I’m not sure if you need to represent progress graphically, or just as a text value. If the latter, a custom formula might also do the trick.