Use the online service or postal form to apply to reduce your Self Assessment payments on account.
You can apply to reduce the amounts you’ve been asked to pay if:
You must claim by 31 January after the end of the tax year - for example by 31 January 2017 for the year 2015 to 2016.
Appeal a penalty using the online form or read guidance on how to appeal.
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Understand your Self Assessment tax bill
Details on when and why you have to make payments on account for Self Assessment.
Don’t include personal or financial information like your National Insurance number or credit card details.