HMRC will use the information in your tax return to calculate the amount of tax that you owe for the tax year, and Class 4 National Insurance if you are self-employed. If you file your return on-line, the amount is calculated automatically just before you file the return and you can view, save, and print the information.
If you file a paper return by the due date of 31st October, HMRC will send you a calculation of the tax due. If you file a paper return after the due date, HMRC will still calculate the tax due, but this could be after the date on which the tax should be paid and interest will still be charged on any tax paid late.
The calculation uses the information you provide in the tax return, which is not checked by HMRC at this stage. This means that if you have made a mistake in the return, the tax you are asked to pay may be incorrect.
It is advisable to check the calculation carefully and if the amount of tax due or repayment is not what you expected, it would be wise to review your return in detail to make sure that you have correctly entered all details of income, expenses, and tax reliefs.
When tax should be paid: self-assessment
The due date for tax is 31st January after the end of the tax year: for the tax year to 5 April 2024, tax should be paid by 31st January 2025 and interest will be due from that date on any late payment.
If your return is filed on time, HMRC will notify you how much tax to pay, but they do not send reminders and it is your responsibility to pay on time. If for any reason HMRC have not notified you how much tax should be paid, it is still your responsibility to pay tax by the due date and interest will be charged on late payment. If you have not filed your return in time, tax is still due on 31st January with interest on late payment. Making an estimated payment by the due date will reduce late payment interest.
Payments on account
If your self-assessment tax for the year is more than £1,000, you will also have to make payments on account for the following tax year. The payments on account are due on 31st January and 31st July and each payment is 50% of the tax due in the previous tax year.
Payments on account apply only after you have filed your first self-assessment return. You will then need to pay both your tax liability for the first year and first payment on account for the second year on 31st January. For later years, the tax due after you file the tax return should be lower, because two payments on account will have been made during the year.
Interest on late payments also applies to payments on account.
If you think your income will be lower in the next tax year, you can apply to reduce your payments on account at any time, but interest will be charged from the original due date if you reduce your payments by too much.
