By
August 8, 2026
Self Assessment Tax Return UK
If you are self-employed, a sole trader, a landlord, receive certain types of untaxed income or have other taxable income that is not fully dealt with through PAYE, you may need to complete a Self Assessment tax return in the UK.
Self Assessment is the system HM Revenue & Customs (HMRC) uses to collect Income Tax from individuals whose tax cannot be collected entirely through other methods.
Understanding whether you need to file, what records to keep and when payments are due can help you avoid unnecessary penalties and stay compliant with HMRC.
This guide explains how Self Assessment works in the UK and the key points taxpayers should know.
A Self Assessment tax return is used to report certain income, expenses, gains and other relevant information to HMRC.
HMRC then uses this information to determine the tax you owe, although when filing online the system will normally calculate the amount based on the information entered.
Self Assessment is commonly associated with self-employed people, but it can apply in many other circumstances.
Whether you need to submit a tax return depends on your individual circumstances.
People who may need to complete Self Assessment include:
There are also circumstances where a person may choose or need to submit a return to claim particular tax reliefs.
Because the rules and thresholds can change, check the current HMRC requirements for the relevant tax year.
Self Assessment is particularly important for sole traders.
Unlike employees whose Income Tax is generally deducted through PAYE, sole traders normally need to report their business income and allowable expenses to HMRC.
For example, suppose your business records show:
Business income: £70,000
Allowable business expenses: £25,000
The starting point for the trading profit calculation would be:
£70,000 − £25,000 = £45,000
Further tax rules and adjustments may apply before determining the final taxable amount.
This is why accurate bookkeeping is important throughout the year.
Operating a limited company does not automatically mean every director must file a Self Assessment tax return solely because they are a director.
However, a director may need to submit one because of their wider personal tax circumstances.
For example, Self Assessment could become relevant where an individual has taxable income or gains that need to be reported separately.
It is important to distinguish between the company's tax obligations and the director's personal tax obligations.
A limited company deals with its own accounts and Corporation Tax, while Self Assessment relates to the individual's personal tax affairs.
The UK tax year generally runs from:
6 April to 5 April
For example:
2025/26 tax year: 6 April 2025 – 5 April 2026
Income and relevant expenses arising during the applicable tax year are used when preparing the corresponding Self Assessment return, subject to the rules that apply to the particular source of income.
Understanding which tax year a transaction belongs to is important when preparing your return.
Self Assessment has several important deadlines.
For most taxpayers filing an online return, the main filing deadline is normally 31 January following the end of the relevant tax year.
Paper tax returns generally have an earlier deadline.
The deadline for paying tax due is also commonly 31 January, although additional payments may be required at other times under the payments-on-account system.
Always check the current deadline directly with HMRC for the tax year you are filing.
If you need to complete Self Assessment and have not previously registered, you may need to register with HMRC.
The process depends on why you need to file.
For example, registration for a newly self-employed sole trader can differ from registration for someone who needs Self Assessment for another reason.
After registration, HMRC may issue a Unique Taxpayer Reference (UTR).
Your UTR is an important identifier used in relation to your Self Assessment tax affairs.
UTR stands for Unique Taxpayer Reference.
It is normally a 10-digit number issued by HMRC to identify an individual or entity within the relevant tax system.
You may need your UTR when:
Keep your UTR secure and readily accessible for tax administration.
The information required depends on your circumstances.
You may need records relating to:
Not every section applies to every taxpayer.
Self-employed individuals should maintain accurate business records throughout the year.
These can include:
Good bookkeeping makes completing a tax return considerably easier and helps support the figures reported to HMRC.
Sole traders can generally deduct qualifying business expenses when calculating taxable trading profits.
Depending on the circumstances, potential expenses may include:
However, an expense is not automatically allowable simply because it was paid from a business bank account.
The relevant tax rules must be satisfied.
Many taxpayers complete their Self Assessment return online.
The general process involves:
Taxpayers can also appoint an accountant or authorised tax agent to prepare and submit a return on their behalf.
The amount of tax payable depends on your total taxable income and personal circumstances.
Different types of income can also be taxed differently.
The calculation may consider factors including:
National Insurance may also be relevant for self-employed individuals.
For this reason, your Self Assessment liability is not necessarily calculated simply by applying one percentage to your business income.
Payments on account can surprise people completing Self Assessment for the first time.
They are advance payments towards a future Self Assessment tax bill.
Where the rules apply, payments are generally made in two instalments, commonly around:
31 January
and
31 July
This can mean that a new taxpayer's first January payment is significantly larger than expected because they may need to pay both the balance for the previous tax year and an advance payment towards the next year's liability.
Not everyone is required to make payments on account, and the calculation is subject to specific rules.
Suppose a qualifying Self Assessment liability results in payments on account being required.
Instead of paying only the previous year's outstanding amount, the taxpayer may also be asked to make an advance payment towards the following year's bill.
A second advance payment can then become due in July.
If your income is expected to fall substantially, it may be possible to apply to reduce payments on account.
However, reducing them too far can result in interest becoming payable if the eventual tax liability is higher.
HMRC supports several methods of paying Self Assessment liabilities.
Available methods and processing times can vary.
When making a payment, it is important to use the correct payment reference so HMRC can allocate the money to the correct taxpayer account.
Do not wait until the last moment if your chosen payment method takes time to process.
Missing a Self Assessment filing deadline can result in penalties.
Additional penalties can arise if a return remains outstanding for an extended period.
Importantly, a late filing penalty can potentially apply even where little or no tax is ultimately due.
If you know you need to file, it is therefore important to submit your return on time rather than assuming there will be no consequence because you do not expect to owe tax.
Late tax payments can result in interest and potentially additional penalties.
The consequences can increase the longer the amount remains unpaid.
If you are unable to pay your full tax bill, do not simply ignore it.
HMRC may have arrangements available for taxpayers experiencing genuine payment difficulties, depending on their circumstances.
If you discover an error after submitting your return, it may be possible to amend it within the applicable time limit.
Examples of errors can include:
The method used to correct the return can depend on when the error is discovered and how the original return was filed.
Mistakes can create additional work and potentially result in incorrect tax calculations.
Common errors include:
Maintaining organised records throughout the year can prevent many of these problems.
Individuals receiving rental income may need to report their property income through Self Assessment depending on their circumstances.
Records can include:
Property taxation has specific rules regarding which costs qualify for relief and how certain financing costs are treated.
Landlords should therefore avoid assuming that all property expenses are deductible in the same way as ordinary trading expenses.
UK taxpayers with overseas income may have additional reporting requirements.
Foreign income can potentially include:
International tax can be complex because residence status, double taxation agreements and foreign tax credits may affect the final position.
Professional tax advice may be appropriate where significant overseas income is involved.
Self Assessment may also be relevant when an individual disposes of assets and realises taxable capital gains.
Examples can potentially involve:
Capital Gains Tax has separate rules, exemptions, reporting requirements and deadlines that can depend on the asset involved.
You do not necessarily need an accountant to submit a Self Assessment return.
Many individuals with straightforward tax affairs complete their returns themselves.
However, an accountant can be useful where you have:
An accountant can also help ensure your records are properly organised and relevant reliefs are considered.
The easiest way to reduce the stress of Self Assessment is to prepare throughout the year rather than waiting until January.
A good routine includes:
Good bookkeeping can turn Self Assessment from a major annual task into a relatively straightforward reporting process.
Before submitting your return, consider checking that you have:
A Self Assessment tax return is used to report relevant income, expenses, gains and other tax information to HMRC so the correct tax liability can be determined.
Sole traders may need to register and complete Self Assessment when they meet the relevant HMRC requirements.
For most online Self Assessment returns, the filing deadline is normally 31 January following the end of the relevant tax year. Always check the current deadline with HMRC.
A UTR is a Unique Taxpayer Reference used by HMRC to identify taxpayers within relevant tax systems.
Yes. Many taxpayers file their own returns using HMRC's online services or compatible software where appropriate.
Late filing can result in penalties, while late payment can result in interest and potentially additional charges.
Yes. You can authorise an accountant or tax agent to deal with HMRC and submit your Self Assessment return on your behalf.
Completing a Self Assessment tax return in the UK does not need to be complicated if your financial records are accurate and up to date.
The key is to understand whether you need to file, maintain appropriate records throughout the tax year and prepare your return well before the deadline.
For self-employed individuals and sole traders, regular bookkeeping is particularly important because your business records form the foundation of your tax return.
If your tax affairs involve multiple income sources, property, investments, overseas income or capital gains, consider seeking professional tax advice to ensure your return accurately reflects your circumstances.
