Different countries have different ways of giving a salary range, in some countries I have noticed that the job posting explicitly says "estimated net salary". Now I am wondering about academic jobs in Norway, it is never specified in job postings so there must be a social norm I guess.
According to some online tax calculator website, a gross salary of 650k NOK per year is about 475k net/year. All the post-docs I have seen are around 500k-600k per year but none of them specify if net or gross. The tax rate seems to be around 30%, are these calculation in a good estimate?
This most likely depends on specific department and funding source, but from what I've seen at UiO a postdoc typically earns 32-35.000 NOK a month, net. This seems to be in agreement with the add you linked.