Tax-code (number) not factored into self-assessment calculation

Hi, I'm in the process of completing my 2022/23 self-assessment but confused as to how my tax code factors into the tax calculation. I had a single employment in the year with a final tax code of 2993L (i.e. higher than the default 1257L). The 2993L code has been used by my employer for PAYE, and is shown in my HMRC account as the "closing" tax code for 22/23 tax year. The amount of tax paid through PAYE appears to be correct as per a 2993L code. As others have noted (e.g. https://community.hmrc.gov.uk/customerforums/sa/1923338f-6555-ed11-97b2-00155d9c9a65), the self-assessment tax calculation is based on the default 1257L. I believe that "other expenses and capital allowances" should be used to allow for any expenses in my tax code. What I'm missing is how HMRC arrived at the 2993L coding in the first place. (My tax code was updated during the tax year). Should I be able to access a breakdown of my tax code on-line through my HMRC account? (I no longer receive paper notifications of tax code changes/updates). All I can find on-line is the actual code, but not how it was derived. Thanks!

Hi Colin,
Online will only show you the code, it doesn't provide a breakdown.
If you don't have a paper coding notice which shows the breakdown you will need to contact us to request the breakdown of the code
Income Tax: general enquiries
Thank you.