Self Assessment: the basics

If you are self-employed or a partner in a business partnership, you will need to complete a Self Assessment tax return for HM Revenue & Customs.


2 min read

1. Overview

Self Assessment involves completing a tax return each year. You show your income and capital gains (profits on the sale of certain assets) and claim tax allowances or reliefs on your tax return.

This guide covers how to get a tax return, when to send it back and what happens if you don't.

2. Who needs to complete a Self Assessment tax return?

You will need to complete a Self Assessment tax return each year if you are self-employed or a partner in a business partnership.

Even if you aren't in business, you may need to complete a tax return if your tax affairs aren't straightforward, even if you already pay tax on your earnings through your tax code. There are also other circumstances in which you will always need to complete a tax return - for example if you're:

  • a company director
  • a trustee
  • receiving foreign income

3. How to get a Self Assessment tax return

You need to register for Self Assessment before you can get a tax return. HM Revenue & Customs (HMRC) will use the information you provide to set up the right records for you. They will then send you a ten-digit tax reference, called a Unique Taxpayer Reference. You will need to keep this safe.

HMRC will send you a letter each year, usually in April telling you to complete your tax return. If you haven't received this letter or a tax return by the end of April, you should get in touch with HMRC.

You can send your tax return online or on paper. There are lots of benefits to sending it online. It's quick, easy and you have three months longer to send it. You need to sign up for HMRC Online Services first.

Once you have signed up, you can use HMRC's free Self Assessment service or you can buy commercial software to send your tax return.

The free HMRC service doesn't provide certain tax returns online and you must use commercial software instead. These include:

  • Partnership Tax Return
  • Trust and Estate Tax Return
  • some pages that support the main tax return, such as those for Lloyd's members and ministers of religion

Tax returns you cannot send online

There is currently no commercial software or HMRC service for the following tax returns:

  • SA700 - Non-resident Company Tax Return
  • SA970 - Trustees of Registered Pension Schemes

You have to send these on paper instead. However, the deadline is the same as for online returns - 31 January.

You can find the Self Assessment forms you need on the HMRC website.

4. Self Assessment tax return deadlines and penalties

If you send in a paper tax return, it must reach HM Revenue & Customs (HMRC) by midnight on 31 October. If you miss this deadline you should send your return online.

If you send in your tax return online it must reach HMRC by midnight on 31 January.

You'll have to pay a £100 penalty if HMRC doesn't receive your tax return on time. The later you send your return, the more penalties you're likely to pay.

New businesses may be able to cut their tax bill. Read our guide on Tax advantages for new businesses.

Get the support you need right now

You can connect with us through the contact form, call us or contact your local Business Gateway office.

You might also be interested in

Preventing discrimination and valuing diversity

The equality legislation helps employers understand how to recruit and treat their staff fairly and promotes diversity in the workplace. Having a diverse workforce means better staff retention, therefore reducing your recruitment costs. Your staff would have greater morale, which means higher productivity for your business.

Help for start-ups – The support available for your start up

If you run a start-up business as an entrepreneur, it's helpful to access networking organisations. Some cater specifically for the needs and interests of entrepreneurs who are women, young people, living with disabilities, different ethnic background, and those on low incomes.