High Income Child Benefit Charge

ceepan

After a few years of not claiming Child Benefit, my wife and I started claiming it again at the beginning of the 2024/2025 tax year due to the changes in the thresholds from £50000 - £60000 to £60000 - £80000.  As a result I needed to reregister for Self Assessment.  My P60 became available today so I thought I might as well complete my Self Assessment and get it out of the way.  Child Benefit is the only reason I need to complete Self Assessment.

I had firstly used https://www.gov.uk/child-benefit-tax-calculator to get an idea of how much I should pay back.  It said that I should pay back £796.  That is based on my income from my P60 of £67624.  I also added £240 that I pay to a pension, which it asked for before the tax relief had been adjusted.

When I attempted to complete my Self Assessment, using those same figures (Tax Paid for the year from my P60 is £16246) it claims that I have to payback £958.38.  The only thing different on my Self Assessment is that under the Pension I entered the value of £300 as it asked for it to include the 20% tax relief by taking the amount paid (£240 which is £20 a month) and dividing it by 80 and multiplying by 100. Under the UK Interest I put the total interest I have earned for the year of £400 which is untaxed.

I have 2 children so the value calculated by the form is £2212 for the year.

Can somebody please explain why there is such a big difference?  I expected a slight difference as I believe that even although the £400 of interest is under the £500 allowance I have before paying interest on that, it still has a slight impact on what I need to payback.

Thanks,
Paul