Self Assessment is a fundamental part of the UK tax system. Yet, many taxpayers remain unsure whether they need to file one, what income is included, and what the consequences of late submission are. Whether you’re newly self-employed, a freelancer, a landlord, or someone with untaxed income, understanding Self Assessment is crucial to staying compliant and avoiding penalties.
In this guide, we’ll explain what a Self Assessment tax return is, who needs to file it, what income to report, important deadlines, and how to get help.
What Is a Self Assessment Tax Return?
A Self Assessment tax return is a method used by HM Revenue and Customs (HMRC) to collect Income Tax from individuals whose earnings are not automatically taxed through the PAYE (Pay As You Earn) system.
Self Assessment explained simply: if you earn money that isn’t taxed at source — such as income from self-employment, rental property, dividends, or overseas income — you’re likely required to report that income and pay tax through the Self Assessment system.
Self Assessment Tax Return Meaning
The term “Self Assessment” literally means that it’s your responsibility as the taxpayer to calculate and report your income and tax due. You must file an annual return with HMRC, declaring all taxable income and capital gains, and claiming any reliefs or allowances you may be entitled to.
Who Must Send a Self Assessment Tax Return?
Not everyone in the UK needs to complete a Self Assessment. Typically, you must file a return if in the last tax year:
- You were self-employed as a sole trader and earned more than £1,000.
- You were a partner in a business partnership.
- You earned rental income from property (even if you’re not a landlord full-time).
- You received dividends or savings income above your allowances.
- You had foreign income that is taxable in the UK.
- You earned income from trusts, settlements, or estates.
- You were a company director (unless it was a non-profit and you didn’t receive any income).
- You claimed Child Benefit and your income was over £50,000 (High Income Child Benefit Charge).
- Your income exceeded £100,000, even if you are taxed via PAYE.
Tip: Even if HMRC hasn’t sent you a notice to file, you are legally required to notify them if you meet any of the criteria.
What Is Included in a Self Assessment Tax Return?
A Self Assessment form includes detailed sections where you report different types of income and claim applicable deductions. Here’s a breakdown:
1. Income Sections
- Employment income (even if taxed at source)
- Self-employment profits
- Partnership income
- UK property income
- Dividends and savings interest
- Foreign income
- Capital gains
- Other taxable income (e.g., pensions, annuities)
2. Deductions & Reliefs
- Business expenses
- Charitable donations
- Pension contributions
- Marriage allowance
- Tax already paid or deducted
For self-employed individuals, it’s crucial to keep records of all income and allowable business expenses.
When Are the Deadlines for Filing and Payment?
Missing the Self Assessment deadlines can result in hefty penalties. Here’s what you need to remember:
| Task | Deadline |
| Register for Self Assessment | 5 October following the end of the tax year |
| Paper tax return submission | 31 October |
| Online tax return submission | 31 January |
| Tax payment (any tax owed) | 31 January |
| Second payment on account (if applicable) | 31 July |
For example, for the tax year 2023/24 (ending 5 April 2024), the online return and tax payment deadline is 31 January 2025.
What Happens If I File Late?
Late filing or payment of your Self Assessment tax return can lead to automatic penalties, even if you don’t owe any tax.
Self Assessment Penalties
- 1 day late: £100 fixed penalty
- Up to 3 months late: £10 per day (capped at 90 days – £900)
- 6 months late: Additional 5% of tax due or £300 (whichever is greater)
- 12 months late: Further 5% or £300
Plus, interest on late payments is charged daily.
If you have a reasonable excuse (e.g., serious illness, bereavement), HMRC may consider waiving penalties.
How Do I Register for Self Assessment?
If you’ve never filed a return before, you must register with HMRC.
How to Register
If You’re Self-Employed:
- Use HMRC’s online service to register as a sole trader.
- HMRC will issue a Unique Taxpayer Reference (UTR) number by post.
- Set up your account for online filing.
If You’re Not Self-Employed (e.g., rental income):
- Register via the SA1 form on HMRC’s website.
- Wait for your UTR to arrive by post.
Tip: Register before 5 October of the tax year following when you started earning untaxed income.
How to File a Self Assessment Tax Return
You can file:
- Online through HMRC’s portal (most common and user-friendly).
- By paper form SA100 (only if submitted by 31 October).
- Through a tax agent or accountant (ideal for complex cases).
Online Filing Steps:
- Log in to your HMRC account.
- Navigate to “Self Assessment”.
- Enter income, expenses, and reliefs in the relevant sections.
- Review the calculation of tax owed.
- Submit your return and keep the confirmation number.
Always keep a digital or printed copy of your return and calculations for your records.
What Counts as Self Assessment Income?
“Self Assessment income” includes all untaxed income you’ve received in a tax year. This typically includes:
- Self-employment income
- Rental property earnings
- Foreign income
- Capital gains on investments or property sales
- Dividends and interest above personal savings allowances
- Commission or freelance income
Remember, even if tax has already been deducted (like on bank interest), you may still need to include it.
Self Assessment for the Self-Employed
If you are self-employed, you must:
- Register as a sole trader.
- Track your income and expenses.
- File your return by 31 January.
- Pay tax based on your net profits.
Allowable Business Expenses
Claimable expenses include:
- Office costs (stationery, phone bills)
- Travel costs
- Marketing and advertising
- Professional fees (accountants, legal)
- Equipment or tools
Keeping digital records using tools like QuickBooks or FreeAgent can make filing much easier.
Self Assessment Help Guide – Where to Get Support
If you’re overwhelmed, you’re not alone. Many people seek help when it comes to Self Assessment.
Options for Help:
- Use HMRC’s online guides and videos.
- Hire a qualified accountant (especially for complex cases).
- Contact Quick Tax Returns – we offer fast, affordable, and expert Self Assessment filing in the UK.
Visit QuickTaxReturns.co.uk for reliable help with tax return preparation and submission.
Final Thoughts – Do You Need to File One?
If you’ve received untaxed income during the last tax year — whether through self-employment, property, or investments — chances are, you are required to file a Self Assessment tax return.
Failing to meet deadlines can lead to penalties and unnecessary stress. The process doesn’t have to be overwhelming — especially with the right help and guidance.
Frequently Asked Questions (FAQs)
1. Who needs to do a Self Assessment tax return?
Anyone who earns untaxed income (like self-employed individuals, landlords, or investors) must usually file a return.
2. What are the deadlines for Self Assessment?
Register by 5 October, submit online by 31 January, and make payments by the same date.
3. How do I register for Self Assessment for the first time?
Use HMRC’s website to register as a sole trader or submit an SA1 form if not self-employed.
4. What happens if I miss the Self Assessment deadline?
You’ll face an automatic £100 penalty, increasing with time and unpaid tax.
5. Can I get help filing my return?
Yes. Services like Quick Tax Returns offer expert assistance to ensure accurate and timely filing.
Need help with your Self Assessment tax return?
Get in touch with Quick Tax Returns today and let our experts handle your tax stress-free.