Self Assement

Hi - I recently submitted my self assessment for 22/23 and have been told I underpaid - this I accept as I earned slightly over the child benefit allowance. HMRC now want a payment of £1000+. However, in the tax calculation HMRC are using the standard allowance of £12,570, but for the entire period I was under tax code 1383M with an allowance of £13,830. That's a significant difference. I called and questioned this and was told 'that doesn't matter' - I can't understand this, surely my tax-free allowance should be measured against the tax code that applied at the time? Any advice on how to appeal the underpayment and get the allowance/code issue recognised please?

Hi

The additional allowance in your tax code would be for the marriage allowance transfer.
If your income for 2022/23 meant you were a higher rate tax payer at 40% then you would not be entitled to the marriage allowance transfer.
To check if this was the case we wpuld need to review the Self Assessment calculation.
You can contact HMRC to check this at Self Assessment: general enquiries

Thank you