tax season has never been good to da god

[Objective]

I swear to God the tax stuff you guys have to do every year is made difficult on purpose so most people have to pay something back, at least that's what it seems like as an outsider. It can be difficult here in Norway as well, a friend of mine had to pay 3700$ back one year but that's only because he forgot to raise his monthly % of tax to 40% instead of 36% when he got a raise which is fairly easy to do if you just remember to do it once you expect to earn more than your usual salary.

I'm wondering tho. Is this something you do once a year? Is there any online calculators to help you out? Do some workplaces do this for you at all, or are you expected to do it on your own? Is it difficult to get it right every year and is it something that takes a whole day to go through? From what I've seen from media and movies it seems like a huge hassle compared to here but I might be wrong.