Personal Allowance (Marriage Allowance) - Self Assessment

I'm completing a self assessment return for the first time due to needing to pay the High Income Child Benefit charge. The calculation for my owed payment is not taking into account my Marriage Allowance and its impact on my personal allowance, meaning the charge due is much higher than I was expecting. Where can I input details of the Marriage Allowance on the self assessment return so that, effectively, my tax code is recognised as 1389M? Thanks

Hi,

Marriage Allowance only shows once the return has been submitted and the calculation will be amended if you are eligible.

Thank you.