Payments on Account

Morning, First time i've done a SA, and have come back with income over £1000. This incurs the requirement of having to honour 'Payments on account'. So, for example, My calculated tax is £1500 for tax year 21 to 22. My payment on accounts are 750 twice. Why is the HMRC asking me to pay an additional year of tax? I don't really understand why i have to pay another years worth of tax as 'Payment on accounts'? Is this a law of some kind? Can i rebute it? And how do they calculate the amount needed for Payments on Accounts? Thanks

Hi,

For a detailed explanation of how the Self Assessment 'Payments on Account' system operates, please refer to the following guidance:  

Understand your Self Assessment tax bill

Self Assessment: the legal framework

Thank you.