How to fill in a self-assessment tax return?

Filling in a self-assessment tax return can be daunting, especially if you’re new to it. But it’s a necessary process that must be done accurately and on time to avoid any penalties. Whether you’re self-employed, a company director, or an individual with multiple sources of income, filing your tax return can seem overwhelming. But fear not; this article will guide you through the process.


What is a self-assessment tax return?

A self-assessment tax return is a document that individuals or businesses must fill in and submit to HM Revenue and Customs (HMRC) to declare their income, expenses, and other details that are relevant to their tax situation. Self-assessment tax returns are used to calculate how much tax an individual or business owes or how much tax should be refunded. If you are required to complete a self-assessment tax return, you must do so accurately and on time to avoid any penalties.


Who needs to fill in a self-assessment tax return?

If you are self-employed or sole trader, a company director, or have additional income or capital gains, you will likely need to complete a self-assessment tax return. If you are still determining whether you need to file a self-assessment tax return, you can check with HMRC or speak to an accountant.

How to fill in a self-assessment tax return?

How to Register for Self-Assessment

Before you can file your self-assessment tax return, you must register for the service. You will need your National Insurance number, personal details, and a valid email address to register.

To register for self-assessment, follow these steps:

  • Go to the HMRC website and select ’Self Assessment’ from the drop-down menu.
  • Click on the ’Register for Self Assessment’ link.
  • Follow the prompts and enter your personal details, including your name, address, and National Insurance number.
  • HMRC will send you an activation code by post within 10 working days.
  • Once you have received your activation code, return to the HMRC website and enter the code to complete your registration.
  • You can then log in to your HMRC account and file your self-assessment tax return.

How to fill in your self-assessment tax return?

Once you have registered for self-assessment, you can begin filling in your tax return. Here is a step-by-step guide to help you complete the form accurately and on time.

Gather your information

Before filling in your tax return, you must gather all the necessary information. This includes:

  • Your National Insurance number
  • Details of your income, including any employment income, self-employment income, pensions, savings, and investments
  • Details of any expenses you can claim tax relief on, such as business expenses or charitable donations
  • Details of any benefits you have received, such as Child Benefits or Tax Credits
  • Any other relevant information, such as capital gains or losses

Choose your filing method

There are two ways to file your self-assessment tax return: online or by paper. Filing online is the most common method and is also the easiest and quickest way to complete your return. To file online, log in to your HMRC account and follow the prompts.

Complete your personal information

The first section of the self-assessment tax return asks for your personal information, including your name, address, and National Insurance number. Ensure you enter this information accurately, as it will be used to identify you and your tax return.

Declare your income

The next section of the tax return asks for details of your income. This includes income from employment, self-employment, pensions, savings, and investments. You will need to enter the total amount you earned for each source of income.

Claim your allowances and deductions

In this section, you can claim any tax allowances and deductions you are eligible for. This includes your personal allowance, which is the income you can earn before you start paying tax, as well as any other allowances such as marriage allowance, blind person’s allowance, or trading allowance.

You can also claim tax relief on specific expenses, such as business expenses, charitable donations, or pension contributions. Ensure you have all the documentation to support your claims and enter the amounts accurately.

Declare your taxable benefits

If you have received any taxable benefits, such as company cars or medical insurance, you must declare them in this tax return section.

Declare your capital gains or losses

You may need to declare any capital gains or losses if you have sold any assets, such as property or shares, during the tax year, you may need to declare any capital gains or losses. You must provide details of the assets sold, the purchase and sale price, and associated costs.

Check your tax calculation

Once you have entered all the relevant information, the tax return will automatically calculate your tax liability or refund. Make sure you check this calculation carefully to ensure it is accurate.

Submit your tax return

After you have reviewed your tax return and are satisfied that all the information is accurate, you can submit it to HMRC. If you are filing online, the system will ask you to confirm that you have reviewed and agreed to the information provided before submitting.


Tips for filling in your self-assessment tax return

Filling in a self-assessment tax return can be complicated, so here are some tips to help you along the way:

  • Start early: Don’t leave your tax return until the last minute. Give yourself ample time to gather all the necessary information and complete the form accurately.
  • Keep accurate records: Keep accurate records of your income, expenses, and other tax-related information. This will make filling in your tax return much more manageable.
  • Use the correct forms: Use the correct tax return form for your circumstances. There are different forms for self-employed individuals , company directors, and taxpayers.
  • Get help if you need it: If you are unsure about any aspect of your tax return, or need help completing the form, feel free to seek advice from a professional accountant or tax advisor.


Filling in a self-assessment tax return may seem daunting, but it doesn’t have to be. Following the steps outlined in this article and keeping accurate records, you can complete your tax return accurately and on time. Remember, filing your tax return accurately and on time is important to avoid any penalties. If you need help, seek advice from a professional accountant or tax advisor.

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