Finland is basically “File a report if your income changes enough to affect your tax bracket. You’ll be issued a new taxation statement. Send it to the employer. (If unemployed, don’t bother, the agency who pays you already knows.) Your employer/the agency will send the taxes owed to us. You’ll be sent an annual tax proposal - If you have no deductions, you don’t need to do anything, if you do, then it gets mildly interesting. If you get tax returns, you don’t need to do anything if we have your bank details. If you owe us, oh boy, we’ll let you know, don’t worry.”