Self-assessment calculation not taking into account already-paid underpayment
In June I received a message from HMRC informing me that I had underpaid PAYE tax from the 2025-2026 tax year. This was because my gross income had surpassed £100k but my tax code had not been adjusted to reflect the loss of Personal Allowance.I decided to pay it to them as a lump sum rather than have it deducted from future earnings.
I have now just registered for self-assessment and am in the process of filing my 2025-2026 tax return. There is a section where it asks for PAYE gross income and tax paid from my P60 from that year. However, as the P60 doesn't contain the extra payment I made, the final calculation wants me to pay that extra amount again. Should I just add that amount to the 'tax paid' section, or is there some other way of making it account for this?