How to File a Tax Return in the UK (2025 Guide)

Filing your tax return can feel daunting—especially if you’re self-employed, a landlord, or have foreign income. At UK Bloom, we simplify the process for newcomers and residents alike. How to File a Tax Return in the UK this 2025 guide walks you through everything from registration to penalties, including important deadlines and useful resources.

Who Needs to File a Tax Return?

You must file a Self Assessment tax return with HMRC if in the last tax year (6 April to 5 April), you:

Were self-employed or a sole trader and earned more than £1,000
Were a partner in a business partnership
Earned £100,000 or more in total income
Had untaxed income, such as rental income, dividends, or foreign income
Claimed certain tax reliefs
Are a trustee or a company director with untaxed income

HMRC will not automatically contact you if you’re required to file. It’s your responsibility to register and file on time.

When Is the UK Tax Return Deadline?

Type	Deadline (Tax Year 2024–2025)
Register for Self Assessment	5 October 2025
Submit paper return	31 October 2025
Submit online return	31 January 2026
Pay your tax bill	31 January 2026

Late filing or payment leads to automatic penalties, even if you owe no tax.

How to Register for Self-Assessment with HMRC

If you’ve never filed before, register by 5 October 2025 at the latest.

For the Self-Employed:

Visit the official GOV.UK Self Assessment registration page.
Select “Register if you’re self-employed”.
Provide your full name, address, date of birth, National Insurance number, and business details.
HMRC will post your Unique Taxpayer Reference (UTR) within 10 working days (21 if abroad).
Set up a Government Gateway ID.

For Others (e.g., Landlords, Directors, Foreign Income):

Use the SA1 form to notify HMRC that you need to file a return.

Documents You’ll Need to File

Gather these before you start your return:

UTR number
National Insurance number
Government Gateway login
Income details (P60, P45, invoices, bank statements)
Expenses and receipts (if self-employed)
Pension contributions and student loan statements
Interest/dividends from savings or investments
Details of rental income and allowable expenses
Foreign income records and any double taxation relief documents

How to File a Tax Return in the UK

Filing online is the fastest and most efficient method. Here’s how:

Step-by-Step Process:

Log in to your HMRC online account.
Click on Self Assessment > File your tax return.
Answer HMRC’s questions to determine which sections apply to you.
Enter income and expenses under the correct headings:
- Employment: Add details from P60 or P45
- Self-employment: Enter income and allowable expenses
- Property income: Add rental income, mortgage interest, repairs
Claim tax reliefs or allowances if applicable
Review your return thoroughly
Submit and note the confirmation reference

🧾 HMRC will immediately calculate how much tax you owe or are due as a refund.

How to File by Paper (and Why to Avoid It)

Paper returns must be filed by 31 October. Use form SA100, available to download or order from GOV.UK.

However, filing by paper is discouraged due to:

Delays in processing
No instant tax calculation
No real-time error checking

Unless you are unable to file online due to disability or lack of internet access, go digital.

What Happens After You File

Once submitted:

HMRC issues a tax calculation and summary
You must pay any owed tax by 31 January
If your tax bill exceeds £1,000, you may have to make Payments on Account (advance payments for the next tax year)
If due a refund, it’s usually paid within 5 working days

Track all activity through your online HMRC account.

Penalties for Missing the Deadline

Filing or paying late triggers automatic penalties, even if no tax is owed.

Delay	Penalty
1 day late	£100 fixed penalty
3 months late	Additional £10 per day (up to £900)
6 months late	Further £300 or 5% of tax due
12 months late	Extra £300 or up to 100% of tax due

Late payments attract 3.25% interest (2025 rate) on top of fines.

Help for New Arrivals in the UK

If you’ve recently moved to the UK, you’re likely unfamiliar with the HMRC process. Here are some tips:

Use the UK Bloom Moving to the UK Guide
Set up a UK bank account to manage tax payments
Apply for your National Insurance Number as early as possible
Read our full article on UK Income Tax Bands and Thresholds for 2025

You can also call the HMRC helpline on 0300 200 3310 for real-time support.

Useful Internal and External Links

External Resources:

Register for Self Assessment – GOV.UK
File your tax return – HMRC
Tax Return Deadlines – GOV.UK
National Insurance – GOV.UK
Foreign Income and Tax – GOV.UK

Frequently Asked Questions

Can I file a UK tax return without a UTR number?

No. You must have a Unique Taxpayer Reference before filing. Apply early to avoid delays.

What if I made a mistake on my tax return?

You can amend your return within 12 months of the filing deadline. Log into your HMRC account and choose the ‘Amend Return’ option.

Do I need to file a return if I’m employed full-time?

Not unless you have additional untaxed income or meet the criteria under Self Assessment.

What happens if I miss the 5 October registration deadline?

You can still register late, but may face penalties or delays. Always inform HMRC as soon as possible.

Disclaimer

This article is for informational purposes only. Always consult the UK Home Office, HMRC, or a licensed tax advisor for personalised guidance. Rules and thresholds are subject to change.