A Self Assessment tax return is one of the most important tax documents you’ll be dealing with if you’re self-employed or earn additional income. Find out if you need to file one for the current tax year and ensure yours is submitted successfully.


What is a Self Assessment tax return?

HM Revenue & Customs (HMRC) collects tax automatically from salaries, wages and pensions. A Self Assessment or personal tax return is a way for HMRC to collect tax from people with income that doesn’t fall under these categories, such as contractors and company directors.

Your Self Assessment is submitted after the end of the tax year it applies to. The tax year runs from 6 April to 5 April the following year. If you have to file a Self Assessment tax return for the 2019/20 tax year, you may do so from 5 April 2020. The due date for filing this return would be 31 January 2021.

Who needs to complete a Self Assessment tax return?

If you receive income that is not taxed at source, you probably need to complete a Self Assessment tax return. There are other reasons too. If in the last tax year you:

  • Were self-employed
  • Became a company director
  • Received income from savings, investment or property
  • Had to pay Capital Gains Tax
  • Received income from trusts, settlements and estates
  • Had an annual income of £100,000 or more
  • Received income from overseas

HMRC may require that you complete one for other reasons, so if you’re unsure, it’s better to get advice from an accountant.

How to submit a Self Assessment tax return to HMRC

If you have never sent a Self Assessment tax return before, you’ll need to register with HMRC first. You need to register by 5 October.

How you register is dependent on your circumstances, such as if you’re self-employed or not self-employed and need to declare income. You must also keep your bank statements and receipts so that you can fill in your tax return correctly.

These are some of the documents you need to fill out your tax return:

  • A P60 from your employer
  • A P45 if you have left a job in the current tax year
  • A P11D or P9D which shows benefits and expenses
  • A summary of rental income and expense
  • Savings and investment statements
  • Documents detailing your self-employment income, including all receipts and bank statements

You can submit your return online or by post. If you do decide to send a paper tax return, make sure to keep a copy of your completed forms and proof that you’ve posted it.

Have a question about your Self Assessment tax return?

Email our expertsLeave a comment below

What are the important Self Assessment deadlines?

What needs to be done

The deadline

Register for Self Assessment

5 October

Paper tax returns

Midnight 31 October

Online tax returns

Midnight 31 January

Payment of tax owed to HMRC

Midnight 31 January

Any outstanding taxes must be paid before 31 January. If you miss the deadline for submitting your tax return, you will be liable for a £100 penalty – even if there is no tax to pay.

Why you should use an accountant to file your tax return

Accurate forms

The biggest concern most people have when submitting their tax return is whether they have filled in their form correctly. These are valid fears as the figures you enter need to be as accurate as possible, and mistakes can be costly.


The process of completing your tax return can be complex and frustrating, which is why it’s often left to the last minute. Like most tax issues, understanding the process and system is time-consuming.

Knowledge of the field

Enlisting the help of an experienced accountant will ensure that your return is completed correctly and on time. He or she will have completed countless tax returns and knows exactly what’s involved. Tax legislation changes all the time, so using an accountant who’s up to date and knowledgeable gives you one less thing to worry about.

Reduce your costs

An accountant may even help you save money by finding ways to reduce your tax bill and prevent you from paying too much tax. They can offer specialist advice and help you manage your finances efficiently.

If you need accounting advice or would like us to assist with your Self Assessment tax return, contact us at contracting@sableinternational.com or call +44 (0) 20 7759 7530.

We are a professional services company that specialises in cross-border financial and immigration advice and solutions.

Our teams in the UK, South Africa and Australia can ensure that when you decide to move overseas, invest offshore or expand your business internationally, you'll do so with the backing of experienced local experts.