When is the deadline to file your tax return?
You should submit your tax return for the year by the 31 January (31 October for paper tax returns) following the end of the tax year, finalising your tax liability from which the two interim payments will be deducted.
If your liability has increased in comparison to the previous year, there will be a balancing payment due. On the other hand, if your liability has fallen in comparison to the previous year, then you will have paid too much and a repayment will be due from HMRC. It’s important to note that if you know well in advance that your taxable income is going to decrease, then you may reduce your interim payments on account, improving your cashflow over the year.