What is a Self-Assessment Tax Return Form?

When you are self-employed or have received untaxed income like rental income or dividends, it is your responsibility to declare your untaxed income and work out your own taxes for HMRC.

The way you report this information to HMRC is with a self-assessment tax return form.

It’s a really important part of your financial administration and any misunderstanding or missing the strict deadlines could result in hefty penalties.

What is a Self-Assessment Tax Return Form?

A self-assessment tax return form is used by HMRC to collect taxes owed by individuals who have received untaxed income.

For many people who are employed, their employer handles on their behalf. Working out how much tax they need to pay, deducting it from their pay and sending it to HMRC for them.

In certain circumstances, individuals receive income that has had no tax deducted from it. But this income is taxable.

These people need to report these earnings on a self-assessment tax return.

A self-assessment tax return form is a summary of everything a person has earned during one complete tax year.

It also includes a tax calculation, so that HMRC know how much tax and national insurance needs to be paid to them.

A tax year runs from 6 April to 5 April.

Will HMRC Tell Me If I Need to Do a Self-Assessment Tax Return?

No, HMRC will not tell you if you need to do a tax return. This is because most UK taxpayers do not need to do one as they work for someone who handles their tax and national insurance for them.

It is your responsibility to check whether you need to do a self-assessment tax return and let HMRC know to expect one from you.

Do I Need to Do a Self-Assessment Tax Return?

You’ll need to do a self-assessment tax return if you have received any untaxed income.

This can be daunting to work out.

You’ll need to do a self-assessment tax return if you have received money from things like:

  • Renting a property;
  • Self-employment and have received income of £1,000 or more;
  • Dividends;
  • Capital gains for example on the sale of a buy-to-let property;
  • Bank interest;
  • Pensions.

Some UK individuals need to file a tax return because they have not received untaxed income but want to:

How Do I Get a Self-Assessment Form?

You get a self-assessment form once you have registered with HMRC.

When Should You register for Self-Assessment?

The deadline for registering for self-assessment is 5 October following the end of the tax year you began receiving untaxed income.

So if you go self-employed on 1 January 2019, you’ll need to register with HMRC by the 5 October 2019.

How to Register for Self-Assessment

The easiest way to register to get a self-assessment form is to go online:

  1. Visit the HMRC website and choose the option to “Register Online”;
  2. Set up your HMRC online account so you can manage your taxes online;
  3. Enrol for self-assessment online;
  4. Wait for your UTR number to be posted to you (can take up to 10 days)
  5. Wait for your activation code so you can complete setup of your HMRC online account.

Need my help registering to get a self-assessment form? Follow this Guide

What is the Self-Assessment Tax Return Filing Deadline?

The self-assessment tax return deadlines vary according to how you file your return and why you need to send one in.

M people now file their tax returns online and the filing deadline for doing so if 31 January each year.

One tax return covers one tax year.

A tax year runs from 6 April to 5 April.

So a self-assessment tax return for 2018/2019 covers the year 6 April 2018 to 5 April 2019 and is due for filing online by 31 January 2020.

Here are all the self-assessment filing deadlines for tax year 2018/2019:

Registering for self-assessment5 October 2020
Filing a paper tax return5 October 2020
Filing you tax return online so HMRC will collect any tax you owe from your wages or pension30 December 2020
Filing online tax returns31 January 2021
Pay any tax and national insurance you owe plus a payment on account, if necessary31 January 2021

A payment on account is a tax contribution towards your following year’s tax bill.

When Can You Submit Your Self-Assessment Tax Return?

You can submit your self-assessment tax return at any time before your filing deadline.

In fact, many people do choose to file their tax return early to stay ahead of the deadline.

Should You Complete Your Self-Assessment Tax Return Online?

Completing your self-assessment online is not only easy, but it also gives you the most time to get it done.

You can also fill in a paper tax return but this needs to be completed and filed earlier, by the 31 October, instead of 31 January.

You can find your self-assessment tax return online in your Government Gateway account.

This is the account you would have set up when you registered as self-employed.

Read this guide if you have lost your HMRC User ID & Password.

Where Can You Get a Paper Tax Return Form?

You can get a paper tax return form by:

  • Downloading it online;
  • Calling HMRC on 0300 200 3310 and asking them to send you a return.

If you are eligible to file a short form tax return (a simplified version of the form) then HMRC will send this to you. You cannot download it or request one.

Don’t forget if you choose to file a paper tax return it is due by 5 October.

What Happens if You Miss the Self-Assessment Tax Deadline?

If you miss the self-assessment tax return deadline, HMRC will issue automatic penalties. You may be able to have these reversed if you have a reasonable excuse.

These start at an immediate £100, rising the longer you leave it. There will also be interest charged on any late payments of tax.

How Do I Fill in a Self-Assessment Tax Return Form?

You can fill in your self-assessment tax return form or get an accountant to do it on your behalf.

But there is no legal obligation to get a professional to do it for you.

That means some people choose to fill out their own return but others prefer to find a professional to do it on their behalf.

It is your responsibility to file your tax return on time otherwise you’ll face penalties.

Many people choose to handle their own taxes and tax returns.

If it is new to you and you’d like to learn more then sign up for my Straightforward Guide to Completing Your Tax Return.

Still unsure? Do You Really Need an Accountant if You’re Self-Employed?

What are the Main Sections of the Self-Assessment Tax Return Form?

A self-assessment tax return form is made up of different sections – the main section and supplementary sections.

The main section of the self-assessment form covers personal information about you and gives HMRC an idea of what income you receive.

Each supplementary section covers a separate form of income or piece of information.

Self Assessment Tax Return Main Section

This section contains details of your personal information such as your:

  • Full name
  • Address
  • National insurance number
  • Date of birth

You’ll also need to use this form to let HMRC know whether you receive income from:

  • Employment;
  • Self-employment;
  • A partnership;
  • UK Property;
  • Foreign income;
  • A trust;
  • Capital Gains.

If you have received any of the above you’ll need to fill out additional pages of your tax return specifically designed for each form of income.

Within the main section of the self-assessment tax return, you’ll also need to declare your income from:

  • Pensions;
  • Annuity;
  • Interest;
  • Dividends.

Self-Assessment Form Supplementary Sections

The supplementary sections available are:

You only need to fill out and include the supplementary sections relevant to you. 

When it comes to completing your tax return online, you’ll only be shown the supplementary pages you need to complete.

This is based on what you ticked in the main section.

Example Self-Assessment Tax Return Form

Here is an example tax return form. This is the paper return to show you what the self-assessment tax form looks like:

Tax Return Example

Self-Employment Supplementary Page Example

The online version is very similar. but is easier to navigate since HMRC splits the return down into bite-sized sections as well as helping you to decide which sections you need.

Step-by-Step Guide to Completing Your Tax Return Online [2018/2019 Edition].

How to Contact HMRC about Self-Assessment

If you have a question for HMRC about registering or the self-assessment tax return form then contact HMRC on 0300 200 3310.

Updated 23 September 2019

Anita Forrest
About Anita Forrest

Anita Forrest is a Chartered Accountant turned entrepreneur who helps the self-employed gain financial confidence when it comes to running the numbers side of their business and filing tax returns with guides, templates and resources on the Go Self-Employed website.