Self-Assessment is the system HMRC uses to collect Income Tax from people whose tax is not automatically deducted at source. If you are an employee or pensioner, your tax is usually handled through PAYE, and you will not normally need to file a return. But if you have other income, or your circumstances fall into one of several categories, you may be required to complete a Self-Assessment tax return each year.
It is your responsibility to determine whether you need to file. HMRC will not always contact you. If you are unsure, HMRC provides an online checking tool to help you find out whether you need to send a return for the current tax year.
1. You Must File a Self-Assessment If Any of the Following Apply in the Last Tax Year
You were self-employed as a sole trader and earned more than £1,000.
The £1,000 figure refers to your gross income before deducting any allowable expenses or tax relief. If your self-employment income was above this self assessment threshold in the tax year, you are required to file.
You were a partner in a business partnership.
All partners in a business partnership must file a Self-Assessment return.
You had to pay Capital Gains Tax
If you sold or disposed of an asset that had increased in value and Capital Gains Tax was due on the gain, how you report and pay it depends on the type of asset. For gains on UK residential property, you must report and pay the tax within 60 days of completion using the UK property reporting service. For other assets, you may be able to use either the real-time Capital Gains Tax service or Self Assessment. That said, even if you have already reported and paid Capital Gains Tax on a property disposal during the year, you will still need to include that gain in your Self Assessment tax return at the end of the tax year.
You had to pay the High-Income Child Benefit Charge, and you do not pay it through PAYE.
If you or your partner receives Child Benefit, and either of you has an adjusted net income above £60,000, a tax charge applies. The charge is 1% of the Child Benefit received for every £200 of income above £60,000, and those earning £80,000 or more repay the full amount. If you pay this charge through the HMRC digital PAYE service, you do not need to file Self-Assessment for this reason alone. If you do not pay it through PAYE, you must declare it through Self-Assessment.
You are an off-payroll worker repaying a student or postgraduate loan.
If you are an off-payroll worker and your engagement falls within the IR35 rules, your student or postgraduate loan repayments may not be correctly calculated through the deemed payment process. In this situation, you will need to file a Self Assessment return so that the correct loan repayment amount can be calculated and accounted for, based on your actual income for the tax year.
HMRC has sent you a notice to file.
If HMRC issues you with a notice requiring you to complete a Self-Assessment return, you must do so even if you do not believe you owe any tax. If you think the notice has been issued in error, contact HMRC to discuss it rather than ignoring it.
Learn to File a Complete Self Assessment Tax Return with Guide:Â How to File Self Assessment Tax Return
2. You May Also Need to File Self-Assessment Tax Return If You Have Untaxed Income
Even if none of the above applies, you may still need to tell HMRC if you have income that has not had tax deducted at source. Whether you need to file a full Self Assessment return depends on the type of income, the amount involved, and whether any allowances apply.
For property income, you generally do not need to tell HMRC if your total rental income is no more than £1,000 in a tax year, as this is covered by the property allowance. Above that level, you may need to report it, but the position depends on your circumstances.
For savings and investments, many people are covered by the Personal Savings Allowance or the Dividend Allowance, meaning tax may not be due at all. If your income from these sources exceeds the relevant allowance, HMRC may be able to collect any tax owed by adjusting your tax code rather than requiring a Self Assessment return.
For foreign income, the rules depend on where you are tax resident, the type of income, and whether a double taxation agreement applies.
In all of these cases, the right starting point is to tell HMRC about the income and let them confirm whether a Self Assessment return is needed or whether the tax can be collected another way. You can use the HMRC online checking tool as a starting point, but if your situation is complex it is worth speaking to a qualified tax adviser.
You May Also Need to Complete Self-Assessment If Your Income Exceeded £100,000
If your total income exceeded £100,000 in the tax year, your tax position can become more complex. This is because the Personal Allowance is gradually withdrawn for income above this level, and in some cases that adjustment cannot be fully handled through PAYE alone.
However, income over £100,000 is not always a standalone trigger for Self Assessment under HMRC’s current guidance, and whether a return is required will depend on your individual circumstances. If you think this applies to you, the best step is to use HMRC’s online checking tool to confirm whether you need to file, or to speak with a qualified tax adviser who can review your position properly.
You May Choose to File Tax Return Even If You Are Not Required To
There are circumstances in which filing a Self-Assessment tax return is optional, but it may be in your best interest. You can choose to file to:
• Claim Income Tax reliefs
• Prove you are self-employed to claim Tax-Free Childcare or Maternity Allowance
• Pay voluntary National Insurance contributions to protect your entitlement to the State Pension and certain benefits
Key Self-Assessment Dates to Be Aware Of
Registering for Self Assessment
If you are new to Self Assessment, or you were previously registered but did not need to file a return last year, you must tell HMRC by 5 October following the end of the relevant tax year. This gives HMRC time to set up your record before the filing deadline arrives.
For example, if you became self-employed for the first time during the 2025/26 tax year, which runs from 6 April 2025 to 5 April 2026, you must notify HMRC by 5 October 2026.
Filing and Payment Deadlines
Once registered, the general deadlines each year are as follows. Paper tax returns must be submitted by 31 October following the end of the tax year. Online tax returns must be submitted by 31 January following the end of the tax year. Any tax owed must also be paid by that same 31 January deadline.
For the 2025/26 tax year specifically, this means your online return and any tax owed are both due by 31 January 2027, and your paper return, if you choose to file one, must be submitted by 31 October 2026.
Payments on Account
If HMRC requires you to make payments on account, these are advance payments towards your next tax bill, split into two instalments. The first payment is due on 31 January and the second on 31 July. For the 2025/26 tax year, the first payment on account is due 31 January 2027 and the second is due 31 July 2027.
A practical example helps illustrate this. If your tax bill for 2025/26 is £3,000 and HMRC determines that payments on account apply, you would pay £1,500 on 31 January 2027 and a further £1,500 on 31 July 2027 as advance contributions towards your 2026/27 liability.
Get Professional Support Early
Many businesses only speak to an accountant when a deadline is looming or something has already gone wrong. Getting advice earlier can help you stay organised and compliant with Self Assessment.
Penalties for Not Filing A Self Assessment Tax Return
Missing a Self Assessment deadline can result in significant penalties, even if you owe no tax at all. The charges build up over time as follows.
Late Filing Penalties
Late Payment Penalties
Interest is also charged on any outstanding balance from the date the payment was due.
When You No Longer Need to File Self-Assessment
If your circumstances have changed and you no longer need to complete a Self Assessment return, you must tell HMRC as soon as possible. Do not simply stop filing without notifying them. If you do, HMRC will continue to expect a return and will issue penalties for missing it, even if you genuinely had no tax to report.
You can notify HMRC online through your personal tax account. HMRC will then confirm in writing whether you are still required to file.
It is important to act early. HMRC specifically warns that if you leave your request too late, particularly close to the 31 January deadline, there is a real risk that your request will not be processed in time to prevent a penalty being issued. If you know your circumstances have changed, do not wait until the end of the tax year to tell them. The earlier you notify HMRC, the better protected you are against unnecessary penalties that can be difficult and time-consuming to challenge after the fact.
Conclusion
Self Assessment applies to a wide range of people, not just the self-employed, but not every change in circumstances or source of extra income means you must file a tax return. It is worth understanding the difference between being required to file, needing to tell HMRC about additional income so they can collect tax another way, and choosing to file voluntarily to claim reliefs or repayments. The responsibility to identify which applies to you, and to register with HMRC by 5 October if a return is needed, rests entirely with you. Missing that deadline or failing to notify HMRC can result in penalties even where no tax is owed. If you are unsure, use the HMRC online checking tool or speak to a qualified tax adviser before the deadlines arrive.
