How to Complete Your Self Assessment Tax Return

Completing your Self Assessment tax return doesn't need to be daunting if you know what information to gather and how to report it correctly. This guide walks you through the process step-by-step, from choosing whether to file online or on paper, to understanding which supplementary forms you need for your specific circumstances.

Should You File Online or On Paper?

97% of people file their Self Assessment tax return online, and there are good reasons for this. When you file online, you get an extra 3 months to submit your return compared to the paper deadline. You can save your progress and return to complete it later, making amendments is easier, and the process is more secure.

You can file your tax return any time from 6 April following the end of the tax year. Filing earlier means you'll know what you owe and can budget accordingly. If you think you'll struggle to pay on time, submitting early gives you time to set up a payment plan.

If you prefer to file on paper, you'll need to download or order the SA100 tax return form and post it to HMRC by the paper deadline.

Before You Start: Registration and Sign-In

If this is your first time filing a Self Assessment tax return, you must register for Self Assessment before you can submit anything. You must tell HMRC by 5 October if you need to complete a tax return for the previous year and you've either not sent one before or registered previously but didn't need to send one for the tax year 2023 to 2024.

If you've registered for Self Assessment in the past but stopped filing, you may need to reactivate your account. Your tax return may be delayed if you file without reactivating an existing account.

To file online, you'll need your Unique Taxpayer Reference (UTR) number and sign-in details for HMRC's online service. You may be asked to prove your identity using photo ID such as a passport or driving licence to keep your details safe.

What You Cannot Do Online

While most people can file online, you cannot use the online service if you:

• Are filing for a partnership
• Are filing for a trust or estate
• Lived abroad as a non-resident
• Need to report multiple 'chargeable event gains' (for example from life insurance)
• Get income from a trust, are a Lloyd's underwriter, or are a religious minister

In these situations, you'll need to use commercial software or complete paper forms instead.

The Main Tax Return and Supplementary Pages

The main tax return form is called the SA100. However, depending on your circumstances, you'll need to complete additional forms known as supplementary pages alongside your main return.

For employment and office holders:

• SA102: Employment (if you're an employee or company director)
• SA102M: Ministers of religion
• SA102MP: Parliament (for MPs)
• SA102MS: The National Assembly of Wales (for Senedd members)
• SA102MLA: Northern Ireland Legislative Assembly
• SA102MSP: Scottish Parliament

For business and property income:

• SA103S: Self-employment (short) or SA103F: Self-employment (full)
• SA104S: Partnership (short) or SA104F: Partnership (full)
• SA105: UK property (for landlords)

For other income and gains:

• SA106: Foreign (for foreign income or gains)
• SA107: Trusts etc (for income from trusts, settlements, or deceased estates)
• SA108: Capital Gains summary (for capital gains and losses)

Other supplementary forms:

• SA101: Additional information (for less common types of income, deductions and tax reliefs)
• SA103L: Lloyd's underwriters
• SA109: Residence, remittance basis etc (for non-UK or dual residents)
• SA110: Tax calculation (for the results of your tax calculation)

What Information You Need

Keep records such as bank statements and receipts so you can fill in your tax return correctly. You need these to report your income and expenses accurately.

You must report various types of income including:

• Self-employment income if you earned more than £1,000 (before claiming any tax relief)
• Money from renting out property
• Tips and commission
• Income from savings, investments and dividends
• Foreign income
• Capital gains when you sold or disposed of something that increased in value

If You Don't Know Your Final Figures

You might not know your exact profit for the whole tax year before the reporting deadline, particularly if your accounting period ends at a different time to the tax year end (5 April), or if you're waiting for a valuation.

In this case, work out what your profit is likely to be using provisional figures and include those in your return. Tell HMRC that you've used provisional figures when you submit. Once you know the actual figures, you'll need to change your return. You have 12 months from the Self Assessment deadline to make these corrections.

If more tax is due, you'll pay interest on the difference from the original payment due date. If you've overpaid, HMRC will pay interest to you.

Common Mistakes to Avoid

• Don't file without reactivating an old Self Assessment account if you've registered before—this can delay your return
• Don't miss the 5 October deadline to tell HMRC you need to file if you're completing a return for the first time or returning after a gap
• Don't forget to include all supplementary pages relevant to your circumstances
• Remember to tell HMRC if you're using provisional figures in your return

Sending Paper Returns

If you complete a paper tax return, post it to:

If you live in the UK:

Self Assessment

HM Revenue & Customs

BX9 1AS

United Kingdom

If you live outside the UK:

HM Revenue & Customs

Benton Park View

Newcastle Upon Tyne

NE98 1ZZ

United Kingdom

HMRC must receive your paper return by the paper filing deadline. If you miss this deadline, send your tax return online instead to avoid a penalty.

Getting Help

HMRC provides detailed guidance notes to help you fill in your tax return. The main guidance document is called SA150 Notes, which runs to 18 pages and explains each section of the return. Each supplementary page also comes with its own guidance.

If you need accessible formats of any forms or guidance (for example if you use a screen reader), email different.format@hmrc.gov.uk and tell them what format you need and what assistive technology you use.

Sources

• Self Assessment tax returns
• File your Self Assessment tax return online
• Complete your Self Assessment tax return for the last tax year
• Self Assessment tax return forms
• Self Assessment supplementary pages

This article provides general guidance based on current HMRC rules. For advice specific to your situation, speak to your accountant.