claim to reduce payment on account

I’m filling my first Self Assessment for the 2023/24 tax year. My incomes in the tax year largely came from bank saving interests. I had huge expenses in the 2024/25 tax year which reduced my savings by one half. As the saving interests I will get in the 2024/25 tax year will be reduced by one half, I would like to claim a reduction in Payment on Account in the 2023/24 Self Assessment. Do I need to attach any supporting documents for the claim in reduction? If yes, what documents should I attach?

Hi,
You do not need to provide any evidence when reducing your payments on account. Confirmation that you were correct to do so comes when you submit your return for the year in which the payments on account were due, and your overall tax liability is calculated. You can see guidance here:
Understand your Self Assessment tax bill
Thank you.