Self Assessment Tax Return 2025/26: Everything You Need to Know Before 31 January 2027

Published: 27 October 2026

Category: Self Assessment | Tax Advice | Self-Employed

If you're self-employed, a sole trader, a taxi driver, a delivery driver or earning income outside your regular employment, understanding your Self Assessment tax obligations is essential.

The deadline for submitting your 2025/26 Self Assessment tax return online is 31 January 2027. Missing this deadline could result in penalties and unnecessary complications with HM Revenue & Customs (HMRC).

At TOPTAX Accountants, we understand that dealing with tax returns can feel complicated, particularly when you're busy running your business. With over 15 years of experience, we help individuals and businesses manage their accounting and taxation responsibilities with confidence.

In this guide, we explain who needs to complete a Self Assessment tax return, which expenses you may be able to claim, the important deadlines and how to prepare.

What Is a Self Assessment Tax Return?

Self Assessment is the system HMRC uses to collect Income Tax from individuals whose tax is not fully collected automatically through PAYE or other arrangements.

If you're employed, your employer normally deducts Income Tax and National Insurance through your wages. However, if you receive self-employed income or certain other types of income, you may need to report these separately.

A Self Assessment tax return allows HMRC to calculate your overall tax position, taking account of your income, allowable expenses, reliefs and any tax already paid.

Who Needs to Submit a Self Assessment Tax Return?

You may need to complete a tax return if you:

• Were self-employed and earned more than £1,000 in gross trading income during the tax year.

• Worked as a taxi driver, delivery driver, driving instructor or freelancer.

• Were a company director with income or gains that require reporting.

• Received rental income from property.

• Received dividends, savings income or other untaxed income requiring declaration.

• Had income from overseas that must be reported.

• Need to report Capital Gains Tax or other relevant tax liabilities.

• Have been asked by HMRC to submit a tax return.

Not everyone in these circumstances automatically needs to file. The requirement depends on your individual tax position.

If you're unsure, it's important to check your obligations rather than assume a return is unnecessary.

Important Self Assessment Deadlines for 2025/26

The 2025/26 tax year covers 6 April 2025 to 5 April 2026.

The main deadlines are:

Important dateWhat it means5 October 2026Deadline to notify HMRC if newly required to register for Self Assessment31 October 2026Deadline for most paper tax returns31 January 2027Online tax return filing deadline31 January 2027Deadline to pay the 2025/26 balancing tax liability31 July 2027Second payment on account, where applicable

If you missed the registration deadline, you should take action as soon as possible. Different filing arrangements may apply to late registrations, but tax payment obligations remain important.

What Expenses Can Self-Employed Individuals Claim?

One of the most important parts of preparing an accurate tax return is identifying legitimate business expenses.

Allowable expenses generally reduce your taxable business profit, meaning you pay tax on your profit rather than your total business income.

Depending on the nature of your business, you may be able to claim:

Vehicle and travel expenses

Fuel, vehicle insurance, repairs, servicing, road tax, business travel and other eligible motor expenses, subject to the method used and the business proportion.

Office and administration costs

Stationery, printing, postage, software subscriptions and other relevant office expenses.

Telephone and internet

The business proportion of mobile phone and internet costs.

Professional fees

Accountancy fees and certain other professional expenses relating to your business.

Advertising and marketing

Business advertising, website expenses and eligible promotional costs.

Equipment and tools

Eligible equipment, tools and other items required for your business, subject to the relevant tax treatment.

Working from home

Where applicable, a reasonable business proportion of eligible household expenses or the appropriate simplified expenses allowance.

It's important to remember that personal expenses are not normally deductible simply because they were paid from a business bank account.

Mileage or Actual Vehicle Expenses?

If you use a vehicle for business, you may be able to calculate allowable vehicle costs using simplified mileage expenses or actual business-related running costs.

For the 2025/26 tax year, the simplified mileage rates for eligible cars and vans were:

• 45p per business mile for the first 10,000 miles.

• 25p per business mile thereafter.

Eligibility restrictions apply, including to certain specialist vehicles such as dual-control driving instructors' cars.

If you use the mileage method, you generally cannot also claim the actual fuel, insurance, servicing and repair costs covered by that rate for the same vehicle.

Choosing the appropriate method depends on your circumstances and any previous claims.

What Documents Do You Need?

Preparing your records early can make the Self Assessment process much easier.

You may need:

• Bank statements covering the relevant tax year.

• Records of self-employed income, including cash receipts.

• Business invoices and expense receipts.

• Mileage records or vehicle expense details.

• P60 or P45 if you were employed during the year.

• Details of pensions, dividends, rental income or other taxable income.

• Relevant HMRC correspondence.

• Details of tax payments already made.

Keeping accurate records helps ensure your tax return reflects your actual financial position.

What Happens If You Miss the Deadline?

Missing the Self Assessment filing deadline can result in an initial £100 late filing penalty, even where no tax is due.

Additional penalties may apply if the return remains outstanding.

Late payment can also result in interest and further penalties.

If you believe you may miss the deadline, seeking advice early can help you understand your options.

Why Submit Your Tax Return Early?

Many individuals leave their tax returns until January, but preparing early offers several advantages.

Know your tax liability sooner

You can understand how much tax you owe and plan your finances accordingly.

Avoid last-minute pressure

There is more time to gather missing records and resolve queries.

Identify potential mistakes

Reviewing accounts and expenses carefully can reduce the risk of errors.

Plan for payments on account

Some taxpayers are required to make advance payments towards the following tax year's liability.

These payments are normally due in January and July, depending on the individual's circumstances.

How TOPTAX Accountants Can Help

At TOPTAX Accountants, we provide straightforward Self Assessment and accounting services for individuals and small businesses.

Our services include:

• Preparation of annual self-employed accounts.

• Self Assessment tax return preparation.

• Calculation of Income Tax and National Insurance.

• Review of eligible business expenses.

• Online submission to HMRC.

• Practical tax guidance and ongoing support.

Whether you're a taxi driver, delivery driver, driving instructor, sole trader or freelancer, we aim to make the tax return process clear and manageable.

We are based in Bradford, West Yorkshire, and support clients throughout the UK.

Self Assessment Services from £150

Our Self Assessment and self-employed accounting services start from £150, depending on the complexity of your circumstances and the work required.

We provide clear quotations before starting work, so you know what to expect.

Need Help With Your 2025/26 Tax Return?

Don't leave your Self Assessment until the last minute.

Whether you're filing for the first time, need help identifying allowable expenses or simply want professional assistance preparing your return, TOPTAX Accountants is here to help.

Contact us today for a free, no-obligation quote.

TOPTAX Accountants

Accounting | Tax | Payroll | Compliance

Call or WhatsApp: 07804 646745

Email: info@toptax.co.uk

Website: www.toptax.co.uk

Based in Bradford – Supporting Clients Across the UK

Clarity over corporate jargon.

Disclaimer: This article provides general information based on UK tax rules applicable at the time of publication. Tax treatment depends on individual circumstances and may change. Professional advice should be obtained where appropriate.