Are Self Assessments Checked?

Hi, For the first time, I was asked to complete a self assessment this year, for 2021-2022. I completed to the best of my knowledge. I didn't earn over £50k net but shows I need to pay £148. I've tried calling to check but never got through. Going to try again tomorrow. Question is, do HMRC check the assessment or not? When I phone, would / could they explain why I have to pay this amount? Thanks for any advice

Hi,

If you have submitted the return we can view the calculation after 72 hours and will be able to advise on why the amount is due.

Thank you.