Do you need to file a self-assessment tax return but are not sure where to start? Well, it might sound complicated. However, it is pretty straightforward once you know the essential steps. In this guide, we will show you how to file a self-assessment tax return in 2025 step-by-step.
What is a Self-Assessment Tax Return?
A self-assessment tax return is how you tell HMRC about your income when it is not automatically taxed. For instance, you can be self-employed, a freelancer, a landlord, or earn money from side gigs.
You report how much you have earned, claim any expenses, and then HMRC determines how much tax you owe. It is usually done once a year, and there are certain self-assessment tax return deadlines to keep in mind.
For example, if you run a small online business selling handmade crafts, you will need to complete a self-assessment tax return to report your sales and any costs. Thus, HMRC will know tax liability.
Who Needs to Complete a Self-Assessment Tax Return?
You might need to complete self assessment returns if any of the following apply to you:
- Your total taxable income was over £150,000.
- You earn more than £1,000 from self-employment before expenses.
- You received rental income exceeding £2,500 (or between £1,000 and £2,500, in which case it is best to check with HMRC).
- You made untaxed earnings over £2,500 from sources like tips, commissions, or freelance work.
- Your income from savings or investments before tax was £10,000 or more.
- You sold assets such as shares or a second home and need to pay Capital Gains Tax.
- You are a company director (except if the company is a charity or non-profit).
- Either you or your partner earned above £60,000 and are claiming Child Benefit.
- You live abroad but have a UK income, or you have to pay foreign income tax.
- You manage a trust or a registered pension scheme as a trustee.
- Your only income was the state pension, but it was higher than your allowance.
- HMRC sent you a P800 showing you underpaid tax last year.
Additionally, if you earned over £50,270 in the 2024/25 tax year and make pension contributions, you can claim extra tax relief through self-assessment tax return. However, if you are on PAYE, you can call HMRC directly.
There is also another option you can choose: filing a self-assessment to pay Class 2 National Insurance contributions. In this way, you can qualify for benefits like the State Pension.
When Do You Need to Complete a Self-Assessment Tax Return?
For the 2025-2026 tax year, here are the key dates to remember when filing your self-assessment tax return:
- 5 April: The tax year ends.
- 31 July: You might need to make a second payment for the previous year.
- 5 October: Register for self-assessment if HMRC has not asked you to, but you need to file.
- 31 October: Last day to send a paper tax return.
- 30 December: File online if you want tax taken from your PAYE code (only in some cases).
- 31 January: Final deadline to file online and pay any tax you owe.
- Up to 1 year after 31 January: You can fix mistakes on your tax return.
How to Fill in a Self-Assessment Tax Return Online?
Now that we have covered the necessary information you need to know, it is time to move on with the steps to filing your self-assessment tax return.
Step 1: Register for Self-Assessment
You can file your self-assessment tax return online from here if you are self-employed. Accordingly, you can also file online if you are not self-employed but need to report your income, like rental earnings.
Once you are registered, the online platform will let you see your past tax returns. Plus, you can check and update your details. It also allows you to print your tax calculation and sign up for paperless notifications.
Step 2: Prepare for Your Tax Bill
During your registration process, you will need the followings to get your self-assessment tax bill:
- Unique Taxpayer Reference (UTR) number.
- Your National Insurance (NI) number
- Information about any untaxed earnings from the tax year, such as self-employment income, dividends, and interest
- Documentation of business expenses if you’re self-employed
- Details of any charitable donations or pension payments that could qualify for tax relief
- Your P60 or other proof of income that has already been taxed
3. Submit your Return
Once you have filled in all the details, it’s time to submit your return to HMRC. You can do this online. Make sure to file before the deadline to avoid penalties.
How to File a Tax Return on Paper?
In some cases, you cannot be eligible to file your return online. At this point, you must file a self-assessment tax return on paper.
HMRC may send you a paper tax return automatically after the tax year ends. If you do not get one, you can download the SA100 form from the government website or call HMRC to request a copy.
Sometimes, HMRC may send a short paper tax return. You cannot download this form online. It is only for those HMRC asks to use it. If you get a notice but no full form, you can ask for the short return. Deadlines are the same as for the full return.
How Long Does a Self-Assessment Tax Return Take to Complete?
The time it takes to get your tax refund can vary depending on your filing type. If you are eligible to apply online, your processing time will be within 1-2 weeks.
On the contrary, if you file on paper, it can take up to 4-6 weeks. This period can extend more during busy periods as 31 January comes closer.
How to Fill in the Main Tax Return (SA100)
SA100 is a type of tax form, which is expected to be filed by anyone eligible for self-assessment tax return. During this process, you can begin by understanding notes relevant for each section
1. Income
In this section, you are expected to declare income from sources such as interest earned on bank and building society accounts, and dividends received from shares.
You need to be sure to include any income, whether your tax has already been deducted or not.
2. Pensions, Annuities, and Benefits
If you are retired, you should report the total State Pension you received during the tax year. Also you need to include any other pension payments, such as annuities, before tax.
For benefits, you have to declare taxable ones:
- Incapacity Benefit,
- Jobseeker’s Allowance,
- Bereavement Allowance,
- Carer’s Allowance,
- Industrial Death Benefit.
3. Other UK Income
This part covers any other taxable income that does not fit into the previous categories. It also covers any allowable expenses related to that income and any tax you have already paid.
4. Pension Contributions
You are required to report any payments made into registered pension schemes or employer pension arrangements. It is also necessary when deductions were made after tax.
5. Charitable Donations
To understand, you need to include the total value of Gift Aid donations made to charities during the tax year. Besides, you must report any gifts of shares, securities, land, or buildings donated to registered charities.
6. Blind Person’s Allowance
If it applies to you, you can indicate here whether you are claiming blind person’s allowance.
7. Student Loan Repayments
If you are repaying a student loan via deductions through your employer, you must provide details in this section.
8. High Income Child Benefit Charge
When you or your partner receive a child benefit and your income exceeds £60,000, you must complete this section.
9. Marriage Allowance
You must complete this section to transfer part of your personal allowance to your spouse or civil partner if your income was below the threshold.
Self-Employed Income (SA103)
If you are self-employed, you should report your total income before any expenses. You can list multiple income sources separately. Thus, it helps to identify your main one.
When it comes to expenses, if your turnover is under £90,000, you can just provide a total amount. If it is over £90,000, you should itemise each expense.
Keep in mind, if you use the £1,000 tax-free trading allowance, you cannot claim expenses too.
Income from UK Property (SA105)
Landlords must report rental income separately for furnished holiday lets and other properties. This includes UK and some European lettings.
If you rent out a room in your home, you must check your eligibility for the rent-a-room scheme. If it does, you can save up to £7,500 tax-free per year.
You can claim expenses like rates, insurance, repairs, loan interest, and legal or management fees. But if you use the £1,000 allowance, you cannot claim these expenses.
Capital Gains (SA108)
When you sell assets, like property or shares, you need to declare the total amount you received.
You can deduct costs like the original purchase price and fees related to buying or selling, such as Stamp Duty.
How to Pay Your Self-Assessment Tax Bill?
When the deadline is coming closer, 31 January, you can wonder how to pay your tax bill. Well, there are several ways to make your payment. You can prefer online or telephone banking, CHAPS payments, debit or credit cards, and paying in person at your bank or building society.
If your previous tax bill was over £1,000 and you have not paid most of it already, you will usually be asked to make ‘payments on account’ towards your next bill. These are split into two instalments due by 31 January and 31 July.
Accordingly, if you think your tax will be lower this year, you can request to reduce these payments. On the other hand, if you’re struggling to pay, HMRC offers a “Time-to-Pay” service. It will allow you to spread payments over time provided that you meet certain conditions.
How to Amend Self-Assessment Tax Return?
As tax resident in the UK, if you need to make changes, you have up to one year after the original filing deadline to amend your return.
To amend online:
- Wait 3 days after filing before making changes.
- Log in to your HMRC account.
- Go to “Self Assessment” > “More Self Assessment details” > “At a glance.”
- Select “Tax return options” and choose the year to amend.
- Update the information and resubmit your return.
To amend a paper return:
- Download the form from GOV.UK or request it from HMRC.
- Mark each page with “amendment,” and include your name and UTR.
- Send it to the address on the form (or the general HMRC address if unknown).
- If you miss the one-year deadline, write to HMRC with details of the changes and reasons.
- If you work with an accountant, inform them as soon as possible.
FAQs on Self-Assessment Tax Return
How can I stop filing a Self Assessment tax return?
If you think you no longer need to file a tax return, it is important to inform HMRC as soon as possible.
Do I need to include Universal Credit on my tax return?
Universal Credit is not taxable, so you do not need to declare it on your Self Assessment tax return.
When can I file my Self Assessment for 2025?
You can submit your return anytime from April 6, 2025, until the deadline. If you want your tax to be deducted through your tax code, you should file by 11:59 pm on December 30, 2025. Otherwise, you will need to pay by other methods.
Do I need to keep receipts for my Self Assessment?
Yes, you should keep all your records and receipts in case HMRC asks to see them.
What happens if I don’t file my tax return on time?
If you register late, HMRC will give you a new deadline. It will be usually three months from when they contact you. They will notify you of this date. A penalty of £100 will apply even if you do not owe any tax.
