Self-Assessment is HMRC's system for collecting Income Tax from people whose tax cannot be collected automatically through PAYE. While employed individuals generally have their tax deducted at source by their employer, there are many circumstances in which a Self-Assessment tax return is also required. If you are unsure whether you need to file, this guide sets out the full criteria, including the edge cases that many people overlook. You can also check your position using HMRC's own tool.
The Core Circumstances Requiring a Self-Assessment Return
HMRC requires a Self-Assessment tax return in the following circumstances:
Self-Employment
If you are self-employed as a sole trader, you must file a Self-Assessment return each year to declare your trading income and expenses and pay the Income Tax and National Insurance arising. This applies regardless of your profit level. Even if your profits fall below the personal allowance, you are still required to file a return if you are registered as self-employed.
Partnership Income
Partners in a business partnership must each file their own individual Self-Assessment return to declare their share of the partnership profits. The partnership itself also submits a separate partnership return.
Company Directors
Directors of limited companies may be required to file a Self-Assessment return in certain circumstances. This is typically the case where a director receives dividend income, which falls outside PAYE, or has other untaxed income to declare. Being a director alone does not automatically trigger a Self-Assessment obligation, it is the nature of the income received that determines whether a return is needed. If you are unsure whether your directorship requires a return, your accountant can advise.
Untaxed Income
If you receive income that has not had tax deducted at source, you are required to declare it through Self-Assessment. Common examples include:
- Rental income from a property you let out
- Savings interest in excess of your Personal Savings Allowance
- Dividend income in excess of the dividend allowance (currently £500 for 2026 to 2027)
- Income from overseas sources, including foreign employment income, pensions or rental income
The High-Income Child Benefit Charge
If you or your partner received Child Benefit and either of you had adjusted net income above £60,000 in the tax year, you may be liable for the High-Income Child Benefit charge. The charge is 1% of the Child Benefit received for every £200 of income above £60,000, reaching 100% of the benefit at £80,000. From 2025/26 onwards, HMRC can collect this charge through your PAYE tax code, which means it does not automatically require you to file a Self-Assessment return. However, if your circumstances are complex or you prefer to settle it through Self-Assessment, you can still do so.
Capital Gains
If you have made a capital gain in the tax year that exceeds your annual Capital Gains Tax exempt amount, you must report it through Self-Assessment. This commonly arises on the sale of investment property, shares or other assets. For the 2026 to 2027 tax year, the annual CGT exemption is £3,000.
Foreign Income
UK residents who receive income from overseas, including foreign employment, overseas pensions, foreign rental income or dividends from foreign companies, are generally required to declare this through Self-Assessment. The rules around foreign income can be complex, particularly where a double taxation treaty applies, and specialist advice is often worthwhile.
HMRC Self-Assessment Criteria: The Edge Cases
The £1,000 Trading and Property Allowances
If your self-employment income or rental income is below £1,000 in the tax year, you may be able to use the trading allowance or property allowance to avoid the need to register and file. However, this only applies if your income from the relevant source is genuinely below the £1,000 threshold. Above this level, a return is required.
Employed with Additional Income
If you are primarily employed and have your tax collected through PAYE, you may still need to file a Self-Assessment return if you have additional untaxed income from any source, whether from a side business, rental property, investments or savings above your allowances. HMRC may sometimes collect small amounts of additional tax through an adjustment to your tax code, but this is only available for amounts up to £3,000. If a return is needed, our Self-Assessment checklist sets out what to gather.
PAYE Only Taxpayers
If all of your income is taxed through PAYE and you have no other untaxed income, you generally do not need to file a Self-Assessment return. HMRC removed the income threshold that previously applied to PAYE only taxpayers from 2024/25 onwards, so there is no longer a specific earnings figure that triggers a return in this situation. The key question is whether you have income that falls outside PAYE, not how much you earn through it — HMRC's list of who must send a return sets out the current criteria.
What Is the Self-Assessment Registration Deadline?
If you become liable to file a Self-Assessment return for the first time, you must register with HMRC by 5 October following the end of the relevant tax year. For example, if you need to file a return for the 2025 to 2026 tax year (which ends on 5 April 2026), the registration deadline is 5 October 2026.
Failing to register by this deadline can result in a penalty. At Affinity Associates Isaacs & Co, our tax compliance service handles Self-Assessment registration and filing for clients across the UK, working to a timetable that keeps returns accurate and deadlines comfortable. Get in touch if you would like us to take it on.