Self Assessment Registration 2025/26: Complete Guide
The Self Assessment registration deadline for the 2025/26 tax year is 5 October 2026. If you have untaxed income, such as self-employment earnings or rental income, you must notify HM Revenue and Customs (HMRC) by this date to avoid potential penalties for late notification.
Overview
Self Assessment is the system HMRC uses to collect Income Tax from individuals whose tax is not deducted automatically from their wages. If you have income that has not been taxed at source, you are responsible for reporting this to HMRC via a tax return. This process ensures you pay the correct amount of tax on your total annual earnings.
Before you start
Before you begin the registration process, confirm whether you actually need to send a tax return. You generally need to register if you are self-employed, a partner in a business partnership, or have other untaxed income. You will need your National Insurance number and details of your income sources. If you have registered before but did not send a return for the 2024/25 tax year, you may need to reactivate your account rather than register from scratch.
How to register for Self Assessment
Step 1: Check your eligibility
Use the official HMRC online tool on GOV.UK to verify if you meet the criteria for filing a tax return. This tool helps you determine if your specific income sources require a formal declaration.
Step 2: Access the registration service
Visit the official "Register for Self Assessment" page on the GOV.UK website. Ensure you are using the official government portal to protect your personal data.
Step 3: Provide your business and personal details
Follow the on-screen prompts to enter your information. You will need to provide details about your business activities, your income, and your personal identification information.
Step 4: Receive your Unique Taxpayer Reference (UTR)
Once registered, HMRC will send you a 10-digit Unique Taxpayer Reference (UTR). Keep this number safe, as you will need it to file your tax return and communicate with HMRC regarding your tax affairs.
Step 5: Set up your Government Gateway account
If you intend to file your return online, you must set up a Government Gateway account. This account allows you to access your tax records and submit your return electronically.
Deadlines
For the 2025/26 tax year (which ended on 5 April 2026), the following deadlines apply:
- Registration Deadline: 5 October 2026.
- Paper Tax Return Deadline: 31 October 2026.
- Online Tax Return and Payment Deadline: 31 January 2027.
If you register after 5 October, HMRC may issue a notice with a specific deadline, typically three months from the date of the notice.
What happens next
After you register, HMRC will issue your UTR. You must keep accurate records of your income and expenses throughout the year. When the tax year ends, you will use these records to complete your tax return. If you fail to file or pay by the 31 January deadline, you may be charged late filing penalties and interest on any unpaid tax.