Filing your self-assessment tax return can be simple and easy. Whether you're a self-employed worker, sole trader, freelancer, contractor, landlord, or earning extra income alongside your job, it’s normal to feel unsure at first.
To file a self-assessment tax return, you need to register with HMRC, gather your income and expense records, complete the online form through your Government Gateway account, submit it, and pay any tax due by 31 January.
This guide explains everything in simple steps, from checking if you need to file to sending your tax return online and avoiding common errors.
What are Self Assessment Tax Returns?
Self Assessment tax returns are the forms you use to tell HM Revenue & Customs (HMRC) about your income and any gains for a tax year, and to work out how much tax you owe (or how much refund you can claim).
Do I need to do a tax return?
Many people are not sure if they need to file a Self-Assessment tax return. For the 2024/25 and 2025/26 tax years, the threshold for high-income PAYE earners has risen to £150,000, but you will still need to submit a return if you are:
- Self-employed with a gross income over £1,000.
- A partner in a business partnership.
- Liable for the High-Income Child Benefit Charge.
- Receiving any untaxed income, including rental, foreign, investment income, or income from trusts and estates.
This ensures HMRC knows your total income and calculates the correct tax.
Self-Assessment Checklist
Before you log in and submit your return, it helps to understand how to file your tax return and gather everything you need.
- Your Unique Taxpayer Reference (UTR).
- Your National Insurance number.
- Income details: PAYE (P60/P45), self-employment profits/losses, property income, dividends, interest, etc.
- Records of allowable expenses if you’re self-employed.
- Details of any capital gains or other taxable events.
- Bank statements, receipts, invoices.
When you file self assessment tax return, having the correct figures will make the process much easier.
How to register and submit your tax return online
A step?by?step guide to help you file self-assessment tax return.
1. Register for self-assessment
If this is your first time using the self-assessment system, you’ll need to register before you can submit online. You’ll need:
- A Government?Gateway account.
- Your 10?digit Unique Taxpayer Reference (UTR), which HMRC will issue once you register.
- Your National Insurance number and other identity details (passport, driving licence, payslip, etc.).
- If you register too late (after 5?October, following the tax year end), you may miss deadlines.
2. Gather your information
Before you log in to complete your return, have these details ready:
- Your UTR and Gateway login.
- Records of income: employment (P60/P45), self?employment earnings, rental income, dividends, interest from savings.
- Records of expenses you can claim if you’re self?employed: receipts, invoices, business costs.
- Other information, such as pension contributions, charitable donations or capital gains, if relevant.
3. Log in to your online tax return
Once registered, you can use the HMRC online service to start your return. The steps are:
- Sign in to your Government?Gateway account and select Self Assessment.
- Choose the tax year you are submitting for (for example, 2025/26 for the?6?April?2025 to?5?April?2026 year).
- The online form adapts to your income. Employment-only income is simpler, while self-employment, property, or other income will show extra sections.
4. Review and submit
Fill in your income and expenses carefully, review for accuracy, and submit your self-assessment online to see your tax owed.
- Enter your income and expense figures in the relevant sections. For self?employment, you’ll complete the business income and allowable costs. For property or investments, fill in those sections.
- Double?check your entries: make sure all income sources are included, and expenses are justifiable and supported by records. Mistakes may cause penalties.
- Submit your tax return online. Once submitted, you’ll receive a confirmation reference, and you can see how much tax (and National Insurance if applicable) you owe.
5. Pay your tax bill and keep proof
- The deadline to submit the online return is midnight on 31?January following the end of the tax year. For example, for 2025/26, the deadline is 31?January?2027.
- Pay any tax owed by the same deadline to avoid interest and penalties.
- Keep a copy (digital or printed) of your submission receipt and your payment record in case HMRC asks for proof later.
Key tax dates and deadlines
Filing your self-assessment tax return on time helps you stay on top of your tax responsibilities and avoid extra charges.
- Online self-assessment: The filing deadline is 31 January following the end of the tax year.
Example: For the 2025/26 tax year, the deadline is 31 January 2027.
- Paper self-assessment: The filing deadline is 31 October following the end of the tax year.
How to pay your tax bill
You can pay your self-assessment tax bill in several ways. It’s important to pay on time to avoid interest and penalties, and HMRC also offers options for larger balances.
- Bank transfer: Pay directly from your bank account to HMRC.
- Debit or credit card: Use your card online or by phone.
- Direct debit: Set up a recurring payment to automatically pay your tax.
- HMRC online services: Pay securely through your Government Gateway account.
- Payment plans: For large balances, HMRC may allow you to arrange a payment plan to spread the cost.
What happens after you submit?
Once you file self-assessment tax return, HMRC will:
- Send you a submission acknowledgement.
- Calculate any tax owed (or refund due).
- Once the payment deadline opens, you’ll usually need to pay your tax by 31 January following the tax year.
- If you owe tax and delay payment, you may face interest and surcharges.
Common mistakes to avoid
Understanding how to do tax returns properly can help you avoid these common mistakes and stay on track with HMRC.
- Waiting until the last minute increases system load and errors around the deadline.
- Not registering in time when you become self-employed.
- Entering incorrect figures for income or expenses.
- Failing to keep supporting records.
- Missing additional pages or supplementary forms.
- Ignoring a notice from HMRC that you must submit.
- Missing the deadline, can lead to late filing penalties and interest charges on unpaid tax.
Conclusion
Filing your self-assessment tax return doesn’t have to be stressful. By understanding how to do tax returns, gathering the right information, and submitting your return online before the deadline, you can stay on top of your tax responsibilities and avoid penalties.
If you prefer expert help, we can handle the entire process for you. We help you to file self assessment tax return accurately and on time. Contact us today at 0208 8611685 or email info@phs-uk.co.uk for professional support.
Frequently Asked Questions
You need to file a self-assessment tax return if you earn over £1,000 in untaxed income in a tax year, such as self-employment, side income, rental income, or other earnings not taxed through PAYE.
You may face a late filing penalty, interest on unpaid tax, and additional daily fines if it continues.
The penalty starts at £100 for missing the deadline and can increase over time if not filed.
What is the interest rate for self-assessment tax?HMRC charges interest on unpaid tax from the due date until payment is made; the rate is updated regularly.
You must inform HMRC, and you may still need to file a final self-assessment tax return covering your last business income.
