Self-assessment tax vs personal tax

Hello, I wonder if anyone can assist. I've just completed my self-assessment tax return for the year 22/23. During the period in question, I was employed full-time PAYE and earned less than the £1000 threshold from my secondary, self-employed job. When completing the SA tax return, I used the income/tax figures from my online HMRC personal tax account, as I didn't have my P60 to hand. However, I noticed that when I logged on to my personal tax account that it states I paid too little tax for that period and that I must pay HMRC £300 odd by 31/01/24. This is apparently due to not having paid enough tax on 'benefits in kind' - this was private medical insurance. However, once I then completed the SA tax return in full, using all the correct figures, it states that HMRC actually owe me £86. This was 4 days ago that I completed the return and both accounts still state the same - personal tax account saying I owe £306 for the year, and the SA page saying I'm owed £86. Which is correct? I've been stung with ridiculous charges before (paid £600 in charges for a discrepancy of less than £1) so want to make sure everything is correct. As a side note, if I hadn't checked my personal PAYE account (to get the figures needed to do my SA return), there's no way I would have known that I owed £306 - I've received no letter or email to say as such. How is this possible? Surely if your only income is PAYE then their tax calculations should be correct and I shouldn't need to check to see if I owe money at the end of the year? Or they'd adjust my income tax payments the following year? Thanks in advance!

Hi,

Self assessment will take priority over a PAYE calculation. Any PAYE calculation arising in a tax year where a tax return is required, will be withdrawn and the self assessment calculation taking precidence.  

You will need to contact our self assesment team, to have this issue checked out.

Self Assessment: general enquiries

Thank you.