How to Complete Your UK Self-Assessment Tax Return for 2024/25

The deadline for self-assessment tax returns is fast approaching, and the thought of completing it can be overwhelming. But don’t panic—starting early will not only help you avoid the last-minute stress but will also allow you ample time to gather all the necessary information. If you delay, you run the risk of making mistakes and losing out on tax-saving opportunities.

In this comprehensive guide, we’ll walk you through the process of completing your self-assessment return for the 2024/25 tax year (6 April 2024 to 5 April 2025), with practical tips and essential deadlines.

Deadline for Self-Assessment Tax Returns

• 31 January 2026 – Deadline for online Self-Assessment submissions and payment.
• 31 January 2026 – Any tax due must be paid by this date.
• 31 October 2025 – Deadline for paper tax return submissions (already passed, so you must file online if you haven’t already).

It’s critical to avoid rushing your tax return. If you don’t submit your return on time, HMRC may impose penalties. Plus, if you’re struggling to get all your documents in order, there are fewer phone lines open closer to the deadline, which can lead to delays.

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UK Tax Return Deadlines: Penalties for Late Submissions and Payments

Failing to file or pay your tax return on time can result in significant penalties. Here’s an overview of the penalties you may face and how to avoid them:

Late Filing Penalties

If you miss the UK tax return deadline, you’ll face the following penalties:

• Initial £100 Penalty: Applied if your return is filed late, regardless of the amount due.
• Daily Penalties: After 3 months, you’ll incur a daily penalty of £10, up to a maximum of £900.
• Further Penalties: After 6 months, you’ll face an additional penalty of 5% of the tax due or £300, whichever is greater. Another 5% penalty will be applied after 12 months.

Late Payment Penalties

If you miss the deadline for paying your tax bill, you will face the following penalties:

• 5% Penalty: Applied after 30 days, 6 months, and 12 months for the amount still unpaid.
• Interest Charges: You’ll also be charged interest on the amount owed, which can add up over time.

Failure to Notify Penalties

If you register for Self-Assessment late (after 5 October), or fail to pay your tax bill by 31 January, you may face a ‘failure to notify’ penalty. This penalty is calculated based on the amount of tax still due and will be issued within 12 months after HMRC receives your return.

To avoid these penalties, it’s crucial to file and pay your Self-Assessment tax return promptly.

Who Needs to Complete a Self-Assessment Return?

Not everyone needs to file a Self-Assessment tax return. However, you are required to submit one if any of the following apply to you:

• Self-Employed as a Sole Trader: If you earned more than £1,000 before expenses from self-employment.
• Business Partner: If you were a partner in a business partnership during the tax year.
• Capital Gains Tax: If you had to pay Capital Gains Tax on the sale or disposal of assets such as property, shares, or other investments.
• High-Income Child Benefit Charge: If you or your partner earn more than £60,000 a year and claim child benefit, you need to declare this charge.
• Untaxed Income: If you received income that wasn’t taxed automatically, such as rental income, freelance earnings, income from savings or investments, or foreign income.
• Income Tax Reliefs: If you want to claim income tax reliefs, such as pension contributions, gift aid, or any other allowances,

If you’re unsure whether you need to file, HMRC provides an online tool that helps you determine whether you’re required to submit a return. If you’ve never filed a return before, you must tell HMRC by 5 October 2026.

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Necessary Documents For UK Tax Return

Before you start filling out your Self-Assessment return, you’ll need to gather all the necessary documents. These include:

• P60/P45/P11D Forms: These provide details of your income from employment or pension.
  
• Bank Statements: If you have self-employment income or other untaxed income, you’ll need to provide statements and records.
  
• Tax Certificates: If you’ve received dividends from shares or interest from savings, ensure you have tax certificates to report on your return.
  
• Invoices and Receipts: If you’re self-employed or have other taxable income, ensure you have records of your business expenses, such as receipts for purchases or invoices issued.

Using the HMRC App

To streamline the process, you can use the HMRC app, which is free and secure. The app allows you to:

• Check your unique taxpayer reference (UTR).
• Track your employment income and view your tax records.
• Set reminders for tax payments and submission deadlines.
• Get help from HMRC’s digital assistant if you have questions about your return.
  

Using the app can save you time compared to manually searching for documents or calling HMRC’s customer support, especially during busy periods.

Don’t Forget About Your Side Hustles

If you have any additional income from freelance work, casual jobs (such as babysitting or dog walking), or property rentals, you must report it in your Self-Assessment return.

• Trading Allowance: If you earn up to £1,000 from side jobs (like tutoring, freelancing, or selling goods), you don’t need to pay tax. However, if you earn more than this, you’ll need to register as a sole trader and submit a return.
  
• Property Income: Income from renting out property is taxable, and you’ll need to declare it in your return. You can deduct certain expenses, such as maintenance and repairs, from your rental income.

Tax on Savings and Investments

With interest rates increasing, more people are exceeding their personal savings allowance and need to declare their savings income. Here’s what you need to know:

• Basic-rate taxpayers can earn up to £1,000 in savings interest tax-free.
• Higher-rate taxpayers can earn up to £500 tax-free.
• Additional-rate taxpayers do not have a savings allowance.

Interest earned in ISAs or some NS&I products is not subject to tax, so you don’t need to declare it.

Claiming Pension Tax Relief

If you’re contributing to a pension, you may be eligible for pension tax relief, which can reduce your taxable income. There are two main types of pension tax relief:

• Net Pay Arrangement: Contributions are deducted from your income before tax is calculated, meaning you get relief immediately at your highest rate of tax.
  
• Relief at Source: If you contribute to a personal pension or some workplace pensions, you receive basic-rate relief automatically. However, if you’re a higher-rate taxpayer, you’ll need to claim the additional relief through your Self-Assessment return.

To claim, enter the total contributions you made, including the basic rate relief you received. HMRC will calculate any further relief due to you based on your tax rate.

High-Income Child Benefit Charge

If you or your partner earn more than £60,000 and claim child benefit, you must pay the High Income Child Benefit Charge. This charge is calculated on a sliding scale and reduces the child benefit you receive. If your income exceeds £60,000, the full child benefit will be clawed back.

You can use HMRC’s child benefit tax calculator to estimate your adjusted net income and determine how much charge you owe.

Reporting Crypto Gains

HMRC is increasingly focused on cryptoassets, such as Bitcoin and Ethereum. If you sold or exchanged any crypto during the 2024/25 tax year, you must report any gains or losses in your Self-Assessment return.

• Crypto assets are subject to Capital Gains Tax.
• The Self-Assessment form now includes specific boxes (13.1 to 13.8) to declare crypto gains.

Make sure to keep accurate records of your transactions, as HMRC requires full disclosure of all crypto-related earnings.

Gift Aid Donations

If you’ve made charitable donations under the Gift Aid scheme, you can claim additional tax relief. As a higher-rate taxpayer, you can reclaim 20% or 25% of the donation amount. For example, if you donate £100, the charity claims £125. You can then claim back £25 in tax relief.

Remember to keep records of all charitable donations made throughout the year.

Avoiding Scams

HMRC has warned about an increase in self-assessment scams, including fake emails and phone calls that attempt to steal personal information. If you receive any suspicious messages, don’t click on links or provide personal information. Report any scams directly to HMRC.

How We Can Help File Your Self-Assessment Tax Return

At Apex Accountants, we provide expert support for completing your self-assessment tax return accurately and on time. Here’s how we help:

Filing Your UK Tax Return

We ensure that your Self-Assessment tax return is filed correctly, whether online or via paper. Our team helps you gather all necessary documents (P60, P45, P11D, bank statements, and more) and submits your return on time, avoiding late penalties.

Tax Planning

We offer personalised tax planning to minimise your liability, such as maximising allowances (e.g., personal savings allowance, capital gains allowance) and guiding you on tax-efficient investments. We help higher earners take advantage of tax-saving strategies like income splitting and pension contributions.

Business Support

For self-employed individuals, contractors, and partnerships, we provide expert guidance on managing income from multiple sources, including freelance work and side hustles. Our support covers bookkeeping, tax deductions, and filing returns for sole traders and partnerships.

Whether you’re self-employed, a freelancer, or a business owner, Apex Accountants ensures you remain tax-efficient, compliant, and on top of your financial obligations.

Contact us today to get expert advice and assistance with your self-assessment tax return.

Conclusion

The self‑assessment deadline for the 2024/25 tax year is fast approaching. Filing your return by 31 January 2026 and paying any tax due on time avoids costly penalties. Register early, gather your documents and make use of allowances to reduce your bill. Keep an eye on hidden income sources such as savings interest, side hustles and crypto gains, and remember to claim pension and Gift Aid reliefs. If you need support, Apex Accountants are here to help you navigate the process confidently and stay compliant.

FAQs 

How do I register for self‑assessment?

Register online through HMRC’s site. If you’re new to self‑assessment, you’ll receive a UTR; if you previously filed, reactivate your account. Allow at least two weeks to receive your UTR and activation code. You must tell HMRC by 5 October following the end of the tax year.

What records should I keep and for how long?

Keep evidence of income, expenses and tax reliefs for at least five years and ten months after the submission deadline. This includes invoices, receipts, bank statements, P60s and P45s, dividend vouchers and interest certificates.

Can I submit my return early?

Yes. You can file anytime after the tax year ends on 5 April and well before the deadline. Filing early helps you know your tax liability and budget for payment. If HMRC owes you a refund, you’ll get it sooner.

What happens if I make a mistake?

You can amend an online return up to 12 months after the filing deadline. If you realise you’ve overpaid tax or missed claiming reliefs, amend your return or write to HMRC asking for a refund.

How can I pay my tax bill?

You can pay through online banking, by direct debit, by debit/credit card or via the HMRC app. If you file by 30 December 2025, HMRC may collect tax owed through your PAYE code. Otherwise, pay by 31 January 2026 to avoid penalties.

What if I cannot pay on time?

Contact HMRC as soon as possible. You may be able to set up a Time to Pay arrangement to spread payments. Ignoring the deadline will trigger late payment penalties of 5% of the tax unpaid after 30 days, 6 months and 12 months, plus interest.

How do I protect myself from HMRC scams?

HMRC warns that thousands of self‑assessment scams are reported each year. Beware of suspicious emails, texts and phone calls asking for personal information or offering refunds. HMRC never asks for personal or financial details by text or email. If in doubt, contact HMRC directly via official contact details and report the scam.