Completing a Self Assessment tax return can feel straightforward until you begin dealing with multiple income sources, business expenses, rental income, foreign earnings or payments on account.
Small mistakes may result in an incorrect tax bill, missed reliefs or questions from HMRC. Waiting until the January deadline can also leave little time to find missing records or resolve registration problems.
A UK Self Assessment tax return is used to report income, expenses and gains that have not been fully taxed through PAYE. This guide explains who may need to file for the 2025/26 tax year, the deadlines to remember, the information required and how professional tax support can make the process more manageable.
Self Assessment is the system HM Revenue and Customs uses to collect Income Tax from people whose tax affairs cannot be dealt with entirely through PAYE. Through a tax return, you may need to report:
You may also use the return to claim eligible expenses, allowances, tax reliefs or business losses. The UK tax year runs from 6 April to 5 April. The tax return currently being prepared in 2026 generally relates to income received between 6 April 2025 and 5 April 2026.
You must normally submit a tax return when HMRC cannot collect all the tax you owe automatically.
You will generally need to file if, during the relevant tax year, you:
You may also need to file when you receive untaxed income from property, commission, tips, savings, investments, dividends or overseas sources. HMRC provides a checking service for anyone uncertain about their filing position.
Having additional income does not always mean that additional tax will be payable. The final position depends on the amount and type of income, available allowances and your individual circumstances.
The following deadlines normally apply to a Self Assessment return covering the tax year from 6 April 2025 to 5 April 2026:
Requirement | Deadline |
Register for Self Assessment when required | 5 October 2026 |
Submit a paper tax return | 31 October 2026 |
Submit online to request collection through PAYE, where eligible | 30 December 2026 |
Submit an online tax return | 31 January 2027 |
Pay the balancing tax due | 31 January 2027 |
First payment on account, where applicable | 31 January 2027 |
Second payment on account, where applicable | 31 July 2027 |
HMRC allows people to submit their returns at any time after the end of the tax year. Filing early can provide more time to review the calculation, plan the payment and correct missing information before the deadline.
You may need to register when you have not previously filed a return or when an earlier Self Assessment account needs to be reactivated.
The correct registration route depends on whether you are:
Once registration is complete, HMRC will normally issue a Unique Taxpayer Reference, commonly called a UTR. You will need this reference when managing your Self Assessment account and filing your return.
New taxpayers who need to submit a return for 2025/26 should usually tell HMRC by 5 October 2026. Registering early reduces the risk of delays caused by missing access details or an inactive account.
The information required depends on your income and financial position. Common records include:
You do not normally send every receipt to HMRC with the return, but you should retain sufficient evidence to support the figures reported.
Good record-keeping also makes it easier to identify missing income, duplicate transactions and expenses that may be claimed correctly.
Begin by listing all income received during the tax year.
Do not assume that HMRC already has complete details of your property income, side business, dividends, overseas income or asset disposals. Information appearing in your Personal Tax Account may still need to be checked.
Reconcile your invoices, receipts, bank transactions and accounting records before entering figures.
For sole traders and landlords, trying to recreate a full year of transactions close to the deadline increases the risk of missing income or claiming an expense incorrectly.
Self-employed individuals may deduct eligible business expenses when calculating taxable profit. Depending on the nature of the business, allowable expenses may include:
An expense is not automatically allowable simply because it was paid from a business account. It must meet the relevant tax rules and relate to the business activity.
Depending on your circumstances, you may be able to claim relief for:
This part of the return deserves careful attention. Missing an available relief can result in paying more tax than necessary.
Before submitting, compare the return against your original documents. Check for:
Submitting a return successfully does not necessarily mean that every figure or tax treatment is correct.
Payments on account are advance payments towards a future Self Assessment bill.
They are normally paid in two instalments:
A first-time filer can therefore face a larger-than-expected January payment. The amount may include the balancing tax for the completed year and the first payment towards the next tax year.
This does not mean the same income is being taxed twice. The advance amount is credited against the following year’s tax liability.
Where income is genuinely expected to fall, it may be possible to apply to reduce payments on account. However, reducing them too far can result in interest when the eventual liability is calculated.
A return submitted after the deadline can attract an initial £100 late-filing penalty, even when no tax is payable or the tax has already been paid.
Additional penalties may arise when the return remains outstanding for three, six or twelve months. Interest and separate charges may also apply when the tax itself is paid late.
Anyone who has missed a deadline should normally deal with the return promptly rather than waiting for HMRC to make further contact.
SHRM’s HMRC Tax Investigation Support service may also be relevant where an enquiry has already started, earlier income was omitted or previous returns require professional review.
Making Tax Digital for Income Tax became mandatory from 6 April 2026 for qualifying sole traders and landlords whose combined gross income from self-employment and property exceeded £50,000 in the 2024/25 tax year.
The threshold is scheduled to extend to qualifying income over:
People within the rules generally need to maintain digital records and use compatible software to send quarterly updates to HMRC.
Making Tax Digital does not remove the need to review the overall tax position or pay the final amount due. Sole traders and landlords should confirm whether the rules apply before assuming their existing annual process can continue unchanged.
Some of the most frequent problems include:
The objective should not simply be to submit the return. It should be to submit a return that is complete, supportable and based on the correct tax treatment.
A person with one straightforward source of income may be comfortable preparing a return independently. Professional support becomes more useful when the return includes:
A tax advisor can help establish what must be reported, review the supporting records, apply relevant reliefs and explain the final tax calculation.
The value of professional support is not limited to entering numbers into a form. It also involves identifying issues before submission and helping the taxpayer understand their wider personal tax position.
SHRM Tax Advisors provides practical UK tax and accounting support to individuals, landlords and business owners. Its services include Personal Tax Planning, Corporation Tax Services, International Tax Advisory, Payroll and Pension Management, HMRC Tax Investigation Support and Outsourced Accounting Services. Through its Personal Tax Planning service, SHRM can help clients:
Getting advice before the deadline provides more time to resolve missing information and make informed decisions.
A Self Assessment tax return should provide HMRC with an accurate account of your taxable income, expenses and gains.
The process becomes more manageable when records are organised early, the correct deadlines are understood and every source of income is reviewed carefully. Professional assistance may be especially valuable when the return involves a business, property, overseas income, capital gains or previous filing problems.
For clear and reliable support, speak with SHRM Tax Advisors about your Self Assessment obligations and wider personal tax-planning needs.
This article is intended as general information and does not constitute personal tax advice. Tax treatment depends on individual circumstances and UK tax rules may change. Information reviewed in July 2026.
At SHRM Tax Advisors, we believe that managing your finances shouldn’t be confusing or overwhelming. Based in the UK, we specialise in delivering clear, practical, and reliable tax and accounting services to individuals, landlords, and businesses alike. With over years of experience, our mission is simple: to help you stay compliant, reduce tax stress, and grow with confidence.
