Self-assessment tax returns

What is self-assessment? 

Self-assessment is HMRC’s system for collecting tax on income that hasn’t already been taxed at source. You’ll likely need to file a return if you: 

• Are self-employed 

• Are in a business partnership 

• Receive rental income as a landlord 

• Are a company director who receives dividends 

• Hold significant investments (outside of ISAs) that generate interest or dividends. 

Not sure if this applies to you? You can check your filing obligations on the HMRC website. 

The key filing deadline for the 2024/25 tax year is 31st January 2026 

Your self-assessment return for the year must be submitted, and any tax due must be paid by this date and missing it could result in penalties and interest charges. 

With all the above in mind, it is a good idea to submit your return now and to help you with this, we have outlined some benefits of filing your tax returns early along with some common self-assessment pitfalls and how best to avoid them. 

Why you should submit your return now 

Enhanced cashflow planning 

Opting to submit your tax return earlier in the year will allow you to find out how much tax you owe and therefore allow you to adjust your cashflow accordingly to accommodate the tax payment due.  

It will give you the flexibility to set aside funds and avoid any last-minute surprises if the tax due is higher than you had initially thought. 

More time for tax planning 

Getting a jump on your self-assessment return gives you valuable time to explore the full range of tax reliefs and allowances available to you. 

Filing early also opens the door to expert advice. Accountants are well-versed in the intricacies of the tax system and can help you maximise efficiency while staying fully compliant. With professional guidance, you may uncover opportunities to reduce your tax bill that you hadn’t considered before. 

If you’re a sole trader or in a partnership, you could be eligible to deduct certain business expenses such as costs related to office supplies, travel, or maintaining your business premises. 

Additional reliefs may include tax-free charitable donations and pension contributions made throughout the year, both of which can help lower your overall liability. 

Beyond these, there is a wide range of reliefs worth considering when preparing your return. At Gravita, we’d be happy to discuss your options and help you get started with your 2024–25 reporting requirements. 

Earlier repayments of overpaid taxes 

Filing early means HMRC can begin processing any refund sooner, which is especially helpful during what is typically a more expensive time of year. 

Earlier Access to Financial Services 

Filing your Self-Assessment tax return early can significantly streamline your interactions with financial institutions. Many lenders, mortgage providers, and credit agencies require up-to-date proof of income and tax compliance when assessing applications. By submitting your return well before the 31st January deadline, you gain timely access to your SA302 tax calculation and HMRC tax year overview. These are two key documents often requested during: 

• Mortgage or remortgage applications 

• Loan or credit facility approvals 

• Rental agreements or tenancy checks 

• Business financing or grant applications 

Early filing ensures these documents are available when needed and in turn reduces any delays. 

In summary, as we enter the festive season, few people want the burden of tax return obligations weighing on their minds. Filing your self-assessment return early allows you to close out the year with clarity, knowing your tax liability, having a payment plan in place, and knowing what funds are available to enjoy the new year with confidence 

Common self-assessment mistakes 

Each year, thousands of taxpayers make errors when completing their self-assessment returns and the upcoming season is unlikely to be any different. The good news is that by understanding the most frequent pitfalls, you can take proactive steps to steer clear of them.

Missing the filing deadline 

Those who miss the self-assessment tax return filing deadline will incur an initial £100 penalty with further fines being issued after three months if the tax return is not filed. On top of this, there is an additional 5% surcharge on any tax that is not settled within 30 days of the tax return filing deadline. Further details on the various penalties that could be levied if your tax return is not filed can be found here. During this time, interest will also be accruing on any outstanding tax that should have been paid by the 31 January 2026 deadline. 

Many taxpayers misjudge how long it takes to complete a self-assessment return, which can lead to unnecessary stress as the deadline approaches. Starting early gives you ample time to gather the necessary information and ensure your submission is completed on time. 

If you anticipate difficulty in paying your full tax bill by 31 January, HMRC offers the option to set up a payment plan provided you act in advance. 

Working with an accountant can further streamline the process. By keeping your records organised throughout the year and handling the submission on your behalf, they can help ensure your return is accurate, timely, and compliant. 

Submitting incorrect figures 

Errors can easily occur when rushing through your tax return, which is why it’s essential to allow sufficient time to review your figures carefully. Inaccurate submissions may trigger a HMRC investigation and in cases of deliberate misreporting, could even lead to prosecution. 

Keeping accurate and up-to-date records throughout the year not only reduces the risk of mistakes but also streamlines the filing process when the deadline approaches. 

If you do discover an error after submitting your return, HMRC allows you to make amendments for up to 12 months following the filing deadline. 

Claiming the right tax relief 

Accurately claiming tax relief is essential. Failing to take advantage of available reliefs and allowances can result in paying more tax than necessary, while overclaiming may trigger an HMRC investigation and in severe cases, lead to prosecution. 

Tax legislation is complex and frequently updated, so navigating it correctly requires attention to detail and specialist knowledge. Engaging a chartered accountant can help you optimise your tax position while remaining fully compliant with current regulations. 

Maintaining thorough records of your business expenses throughout the year is equally important. Although you may not need to submit these with your return, they must be readily available should HMRC request supporting documentation. 

Don’t overlook payments on account 

In addition to your tax bill for the 2024/25 tax year, HMRC may require you to make advance payments towards your 2025/26 liability, these are known as payments on account. These payments on account can result in you paying up to 50% more than anticipated on 31st January. 

To avoid unexpected strain on your finances, it’s important to factor this into your budgeting. Filing your return early gives you time to prepare for both the initial payment due by 31st January 2026 and the second instalment, scheduled for 31st July 2026. 

Planning ahead is key. If you expect your income to be lower than the previous year, you can request a reduction in your payments on account via HMRC’s online services. Reviewing HMRC’s guidance will also help you understand your obligations and avoid surprises.

Omitting your child benefit payments from your return. 

If you or your partner have adjusted net income over £60,000, you may need to repay some or all of your Child Benefit through the High Income Child Benefit Charge (HICBC). The charge is collected via Self-Assessment and is calculated at 1% of the Child Benefit received for every £200 of income above £60,000. Once income reaches £80,000, the charge equals the full Child Benefit. 

The higher earner must include Child Benefit on their tax return (unless PAYE collection has been arranged). If omitted, HMRC can amend the return, and interest and penalties may apply if the additional tax is not paid by the Self-Assessment deadline. 

Ensuring the accuracy of your return 

While many individuals opt to complete their self-assessment tax return independently, engaging a qualified accountant can offer significant advantages, particularly if you operate a business or have multiple income streams. Complexities such as mixed-use expenses or varying sources of revenue often require specialist insight to navigate correctly. 

Accurate reporting is essential, and professional support can help ensure your return is accurate, timely, and optimised to minimise your tax liability. Whether you’re a business owner or simply seeking peace of mind, working with a tax adviser can make the process smoother and more efficient. 

What next? 

If you’d like expert support with your self-assessment return, the Gravita team is here to help. Contact us today to speak with one of our advisers.