How do I file my self assessment tax return online in the UK?

Is filing of self-assessment tax return online for your clients taking too much of your time? For self-employed individuals and directors whose income is not deducted at source through PAYE, HMRC has created a self-assessment system. Under this system, it is their responsibility to inform HMRC about their income, expenses, and other sources of income once a year. If your client is earning income from savings or investments, then they are liable to make a self-assessment tax return.

According to UK government statistics, in the year 2023-24 around 11.5 million tax payers filed their self-assessment tax return and 97.36% of tax returns were filed online. You might think that doing self-assessment tax returns online for your clients is a routine task, but that’s not the case. Progressively, it has become a multi-step process and can get time-consuming.  

Here is a step-by-step guide to quicken the online filing process:

1. Registration for Self-Assessment (If not filed before)

If your client is not registered for self-assessment, then please do the needful before the registration deadline on 5th October. You will need to create a government gateway account with a user ID and password for registration.

Once registered, HMRC will send a 10-digit Unique Taxpayer Reference number (UTR) within 10 days, along with an activation code. Use the UTR and activation code to activate your client’s online Self Assessment account.

2. Gather Your Information

Keep all required documents and figures ready in advance to make the process fast and smooth. These records include:

• National Insurance number
• Keep records of your self-employed income and allowable expenses, including invoices, receipts, and accounts.
• Income from property rental, dividends, interest, foreign income, etc.
• Details of any taxable state benefits or pensions.
• Records of pension contributions.
• Records of charitable donations (Gift Aid).

3. Log In and Start Your Return

With the government gateway user ID and password in your hand, you can now sign in to the self-assessment page. Once you have logged in, you will need to enter the relevant sections such as:

SA100 (main section)

Under it, personal details of client such as date of birth, name, address, telephone number, and National Insurance number (updates in 2026) need to be added. Also, to be added are:

SA103 (self-employment)

Under this section, you report your client’s income from employment, such as a director’s salary. Employment benefits and expenses from the employment or directorship can also be declared.

SA105 (UK property)

This section needs to be filled if your client has received more than £1,000 from:

• Rental income and other types of income from UK land or property
• Income from letting out furnished rooms in your own home
• Income from furnished holiday lettings (FHL) in the UK or European Economic Area (EEA)
• Premiums from leasing UK land
• Inducements to take an interest in letting a property (a reverse premium)

4. File Self-Assessment Tax Return

Once you complete all sections, calculate the return and review it carefully one final time. Save the copy and file the self-assessment tax return by 31st January.

5. Pay Tax Bill

If your client owes any tax to HMRC, then it is your responsibility to ensure that the payment is made by 31st January.

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Conclusion

The above steps will help you assist your clients in filing their self-assessment online without any hiccups. Still, if you need any assistance with self-assessment, you can explore outsourcing self-assessment work.

Speaking of professional outsourcing service providers in the UK, you will find Coirent among the top. Through our year-end outsourcing services, your self-assessment will be handled by expert accountants, ensuring full compliance.

If you have any special requests or points to share, please use our contact form, and our staff will connect with you at the earliest. Looking forward to doing business.

Shweta Kemnaik

Shweta Kemnaik is the director of Finance and Accounting at Corient and is currently handling F&A operations. Her 8+ years in the Outsourcing Industry and rendering services to UK-based CA firms have helped her develop new processes and smoothen their accounting and management reporting. Her experience has helped her in meeting quality control requirements and sustaining high customer satisfaction.

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