What is self-assessment?

For many people, income tax is automatically calculated and deducted from their salary before they’re paid. However, some individuals need to file a self-assessment tax return to calculate how much tax they owe.

Here's our guide to help you find out if self-assessment applies to you and what you may need to do.

A self-assessment tax return is a form used to report income, capital gains, and other taxable earnings to HMRC. It helps calculate how much tax you owe.

HMRC provides an online portal for filing your tax return. You can also request a paper version from them if you prefer. 

The deadline depends on how you choose to file your tax return: 

Online self-assessment tax returns must be submitted to HMRC by midnight on 31 January following the end of the tax year. For the 2025 to 2026 tax year, the deadline is 31 January 2027. Any tax owed must also be paid by this date to avoid fines.

Paper self-assessment tax returns needed to be posted. It must reach HMRC by midnight on 31 October following the end of the tax year. For the 2025 to 2026  tax year, the deadline is 31 October 2026. If you miss this deadline, you must file online by 31 January 2027 to avoid fines.

There are 3 factors that influence whether you need to do a self-assessment. These relate to:

If you're on the payroll of the company where you work, the income tax you owe will be taken off your salary before you receive it. This is a system called PAYE (pay as you earn), which means you don't usually have to complete a self-assessment tax return.

But you will need to do a self-assessment if you're either of the following:

You may also need to do a self-assessment on other income including:

Visit GOV.UK: Check if you need to send a self-assessment tax return

There are other reasons why you might need to fill in a self-assessment tax return.

If you receive child benefit, you may need to submit a return if you (or your partner) have an income that’s more than £60,000. This is because you'll have to pay the high income child benefit charge.

Some people also choose to do a tax return so they can claim certain types of income tax relief.

Another reason to complete a self-assessment return might be to prove you're self-employed so you can claim things like tax-free childcare or maternity allowance.

If you're still not sure whether you need to send a tax return, you can contact HMRC for help.

You might need a certificate of interest (tax certificate) to complete your tax self-assessment. This document confirms the total amount of credit interest paid into an account over the tax year. 

If you need a certificate of interest, they are available in the mobile banking app in the account information section. Alternatively, please send us a secure e-message in online banking or by using chat in the mobile app and we’ll post you a copy.

Missing the deadline for filing your self-assessment tax return can result in penalties and additional charges. 

Here’s what to expect:

Important: If you’ve missed the deadline, file your return and pay any tax you owe as soon as possible to minimise fines.

Register and file your self-assessment on GOV.UK

Once you’ve submitted your tax return it, it’s easy to pay your bill using online banking. It’s similar to paying utility bills. Keep in mind that if you're an HSBC customer you'll be able to send up to £25,000 when making mobile or online payments.

To pay online you’ll need to find the relevant bank details for HMRC so you can make the transfer.

The GOV.UK website also has information about other ways of paying such as by Direct Debit, at a bank or building society or by cheque.

For more information, visit GOV.UK: Pay your self-assessment tax bill

This article was last updated: 16/04/2026, 05:00