materialhazard

I am fully employed but fall into the third category of those who need to fill in a tax return--ie. I am neither self-employed nor a partner in a business partnership. As I am fully employed, all of my tax payments are paid via PAYE, and hence I ought to owe no tax on top of what was paid directly by my employer. My problem is that the self-assessment calculator seems to believe I owe money, but I don't think this should be the case. The figures I used are coming from my P60. Am I filling the form out incorrectly or are one / multiple of my assumptions above mistaken? (eg. am I accounting for something like student loan / National Insurance / pension payments incorrectly?) I can't reach anyone via the phone helplines to address this. Many thanks