Are you ready for your self-assessment tax return?

Date: December 11, 2025

Filing a self assessment tax return can seem intimidating, especially if your financial situation has changed or this is your first time completing one. With strict HMRC deadlines and significant penalties for mistakes or late submissions, staying organised and informed is critical.

As deadline day approaches, this guide covers what a self assessment tax return entails, the key deadlines for the 2024/25 tax year, common pitfalls to avoid, and how Alexander & Co can provide expert tax support to ensure your return is accurate and compliant.

What is a self assessment tax return?

A Self Assessment tax return is a method HMRC uses to collect Income Tax from individuals whose tax is not automatically deducted. Unlike PAYE, where your employer deducts tax at source, Self Assessment requires you to report all taxable income, claim eligible expenses, and calculate the tax owed for the year.

Who needs to submit a self assessment return?

You typically need to submit a Self Assessment return if you are self-employed, receive rental income, earn dividends or interest, have pension income, or are a company director with income outside PAYE. Once filed, the information provided will determine your tax liability and set payment requirements.

Key self assessment deadlines for the 2024/25 tax year

The tax year for 2024/25 ended on 5 April 2025. If you are new to Self Assessment, you must register with HMRC by 5 October 2025 to avoid delays and potential penalties. Failing to register on time can complicate your ability to file and create unnecessary fines.

Paper returns were due by 31 October 2025, while online submissions must be completed by 31 January 2026. Any tax due is also payable by 31 January 2026, including the first payment on account for the following tax year, if applicable. Meeting these deadlines is essential to maintain compliance and avoid additional charges.

How to complete a self assessment

The first step is to register for Self Assessment and create a Government Gateway account. Next, collect all relevant financial records, including income statements, bank interest, dividend vouchers, and records of allowable expenses.

Step-by-step process:

Register for Self Assessment and obtain your Unique Taxpayer Reference (UTR).
Gather all financial documents for the relevant tax year.
Complete the online Self Assessment form via HMRC’s portal.
Double-check all calculations and income entries.
Submit your return and arrange payment by the deadline.

Careful preparation reduces the likelihood of mistakes and prevents HMRC from raising queries or penalties later.

Alexander & Co can take care of the process for you, calculating and filing the return on your behalf.

What else do I need to watch out for with the self-assessment tax return?

One of the most frequent errors is failing to report all sources of income, such as freelance work, investments, or rental payments. Claiming expenses that do not meet HMRC’s criteria can also create issues if your return is reviewed.

Additionally, ensuring personal information is current, including addresses and employment details, helps prevent delays or unnecessary communication from HMRC. Small inaccuracies can escalate into more significant problems if left uncorrected.

How do I pay my self-assessment tax?

HMRC provides several payment options, including online banking, debit card, and direct debit. The total amount owed will be displayed once your return is submitted, allowing you to plan your payment ahead of the due date.

If your total tax bill exceeds £1,000, you may be required to make payments on account—advance payments toward the next year’s tax. Planning for these payments early can prevent unexpected financial strain.

What Happens If You Miss the HMRC Deadlines?

Missing the filing deadline triggers an automatic £100 penalty, even if no tax is owed. Additional penalties usually follow if the delay continues.

Late payment also incurs interest from the original due date, and further penalties apply if the balance remains unpaid. Acting quickly and seeking advice early can reduce these costs significantly.

What if my circumstances change?

Changes such as starting a new business, acquiring rental property, or becoming a company director may affect your filing requirements. Informing HMRC promptly ensures you remain correctly registered.

If your circumstances change such that you no longer need to file a return, notifying HMRC prevents unnecessary filings and potential penalties.

Is it hard to do your own self-assessment tax return?

For those with straightforward income sources, completing a Self Assessment may be manageable. However, complexity grows with multiple income streams, investment income, or capital gains.

Many errors stem not from negligence but from misunderstanding tax legislation and HMRC rules. Professional guidance can provide peace of mind and ensure your return is accurate and compliant.

Why is it important to start preparing early?

Starting early gives you time to gather all necessary documents and identify missing information before deadlines approach.

Benefits include:

Better management of tax payments and cash flow
Reduced risk of errors or omissions
Time to seek professional guidance if needed
Lower stress and smoother submission process

When Do You Need to File a Self-Assessment Tax Return?

You usually need to submit a return if you are self-employed, earn rental income, have untaxed earnings, or need to declare capital gains. High earners or those claiming certain reliefs may also have an obligation to file.

If unsure whether you must file, it is best to clarify early to avoid missed registration or late penalties.

How Can Alexander & Co Help You?

Alexander & Co provide comprehensive support for all types of Self Assessment tax returns. From reviewing financial records to preparing and submitting returns, we help ensure compliance with HMRC rules.

Our team works closely with clients to understand their circumstances and provide practical, reliable advice. Whether your tax situation is simple or complex, Alexander & Co can help make filing a Self Assessment straightforward and worry-free.

If you are interested in Alexander & Co completing your tax return on your behalf, please contact us:

Call us today on 0161 832 4841 or 0207 167 7220
Email us at info@alexander.co.uk
Request a call via our Contact Form

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