How to Prepare and Submit Your Self Assessment Tax Return: A Guide for UK Small Business Owners
- Millie O'Neill
- May 27
- 3 min read
Updated: 3 days ago
If you're self-employed, a sole trader, or run a small business, submitting a Self Assessment tax return can feel overwhelming—especially if it’s your first time. But don’t panic. With a bit of planning and the right information, it doesn’t have to be stressful.
Here’s everything you need to know to get it right.
1. Do You Need to Submit a Tax Return?
To ensure longevity and success, small businesses can put in practices that not only enhance customer experience but also streamline operations. Here are key strategies to consider:
You’ll need to submit a Self Assessment tax return if you:
Are self-employed (sole trader) and earned more than £1,000
Are a partner in a business partnership
Have untaxed income, such as rental income, dividends, or investments
Need to claim certain tax reliefs
2. Registering for a Self Assessment Tax Return
First-time filers must register with HMRC. This should be done by 5 October following the end of the tax year you need to file for.
Example:If you need to file for the 2024/25 tax year (6 April 2024 – 5 April 2025), you must register by 5 October 2025.
You can register here: Register for Self Assessment – GOV.UK
3. What You’ll Need Before You Start
Before diving into your tax return, get organised with the following:
Your Unique Taxpayer Reference (UTR) number
Your National Insurance number
Records of all income, including invoices, bank statements, and receipts
Records of allowable business expenses
Details of other income: rental income, dividends, savings interest, etc.
4. Allowable Expenses – What Can You Claim?
Claiming expenses helps reduce your tax bill. You can claim for things like:
Office costs (stationery, phone bills)
Travel expenses (fuel, parking, train fares)
Business insurance
Marketing and advertising
Professional fees (accountant, software)
Use of home as office
Make sure your expenses are wholly and exclusively for business.
5. Understanding Tax Codes and Income Tax Bands
Your tax bill is based on your taxable profit (income minus allowable expenses).
The current (2024/25) Income Tax bands for England & Wales are:
£0 – £12,570: 0% (Personal Allowance)
£12,571 – £50,270: 20% (Basic rate)
£50,271 – £125,140: 40% (Higher rate)
Over £125,140: 45% (Additional rate)
Tax bands can differ in Scotland.
6. What Are Payments on Account?
If your tax bill is over £1,000, HMRC will ask you to make advance payments for the next year. These are called Payments on Account.
You pay 50% of your current year’s tax bill on 31 January
Another 50% on 31 July
If you’ve overpaid, HMRC will refund you. If you’ve underpaid, you’ll owe a balancing payment the following January.
7. Deadlines You Need to Know
Register for Self Assessment: 5 October
Submit paper tax return: 31 October
Submit online tax return: 31 January
Pay your tax bill (and first payment on account): 31 January
Second payment on account (if applicable): 31 July
Missed deadlines can lead to fines, so pop them in your calendar!
8. How to Submit Your Return
You can file your return online through your HMRC account. Here’s how:
Log in to your HMRC online account
Go to Self Assessment
Follow the steps to enter income, expenses, and other income
Submit and pay by 31 January
From next year if you're a sole trader or landlord earning £50k+ you will need to file using the new Making Tax Digital rules (check our our previous blog!)
9. Top Tips to Make It Easier
Don’t leave it to the last minute!
Keep digital records throughout the year
Use bookkeeping software to track income and expenses
Ask for help if you’re unsure—HMRC has a Self Assessment helpline
Work with a bookkeeper and/or accountant for peace of mind
Need Help with Your Tax Return?
If you're juggling everything yourself, getting an accountant might just be the best decision you make in business. At Highlight, we take the stress out of tax so you can focus on what you do best.
Get in touch today—we’re just a WhatsApp away.
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