Self Assessment Deadline Just 10 Days Away: Don’t Make These Mistakes

With just 10 days to go until the Self Assessment deadline on 31 January, many individuals are bracing themselves to complete a task they may have done dozens of times before – completing their Self Assessment Tax Returns.

For many taxpayers, this is a routine task that they think they can get done without any problem. But this exactly what breeds complacency and leads to mistakes, penalties and interest.

Here are some common mistakes people tend to make on their tax returns.

Forgetting Income HMRC Doesn’t Automatically Know About

People have complex financial lives. You may have employment income, private pensions, the State Pension, rental income, dividends, interest or occasional consultancy work. And you may make the mistake of assuming HMRC already knows about everything. While HMRC does receive some information automatically, that doesn’t remove your responsibility to declare all taxable income correctly.

The State Pension, for example, is taxable but not taxed at source. Many retirees overlook it when completing their Self Assessment. Failing to include any income, however small, can trigger HMRC enquiries or fines, and can be extremely stressful to resolve.

Missing Out on Allowable Deductions

Many individuals concentrate on reporting income accurately but pay less attention to deductions and tax reliefs. Overlooking them can result in a significantly higher tax bill than necessary. Commonly missed items include pension contributions that qualify for tax relief, Gift Aid donations, certain professional fees or subscriptions, expenses associated with rental properties and capital losses that can be offset against gains.

Gift Aid is particularly important for wealthier taxpayers because higher-rate relief must be actively claimed through Self Assessment. Failing to claim deductions you are entitled to means simply paying more tax than you need to, year after year. To avoid this, review your bank statements and donation records for the entire tax year. When in doubt, check whether a payment could be deductible rather than assuming it is not.

Not Using Personal Allowances Effectively

For couples, especially in retirement, tax efficiency is often about balance. One partner may be paying higher-rate tax while the other has unused personal allowance or lower tax bands. Failing to split income-generating assets, where legally possible, can lead to unnecessary tax. This is commonly seen with savings accounts, investments or rental income held solely in one name.

By reviewing whether assets can be shared between spouses or civil partners, it’s possible to make better use of both personal allowances and lower tax bands. While this needs to be done properly and ahead of time, taking a moment to review asset ownership each year can have a significant impact on the amount of tax owed.

Falling Foul of Capital Gains Rules

Capital Gains Tax mistakes are very common. Errors often include forgetting to declare gains, failing to deduct allowable costs such as purchase fees, improvement costs or annual exemptions, and assuming incorrectly which assets are sheltered.

Clear records of asset purchases and sales are essential and it’s worth double-checking which wrappers provide tax protection before submitting your return.

What to Focus on in these Final 10 Days Before the Self Assessment Deadline

With the Self Assessment deadline just 10 days away, the key is accuracy over speed. At this stage, rushing through your return will only increase the chance of costly mistakes. Instead of trying to reorganise your finances or claim new allowances, focus on reviewing what’s already entered.

Double-check that all income sources are included, that deductions and reliefs have been correctly claimed, and that any Child Benefit or capital gains charges have been calculated properly. Make sure personal details such as your Unique Taxpayer Reference (UTR) and National Insurance number are correct, as errors here can delay processing or trigger HMRC enquiries.

If possible, consider having professionals like UK Property Accountants review your return before submission. Even a quick professional check can help catch mistakes that might otherwise cost thousands. Remember, at this stage, it’s about submitting a correct and complete return, not reorganising your finances.

Conclusion

With only 10 days to go, there’s no time for complacency, but there is still time to file accurately. Focus on completing your return thoroughly, ensuring every income source is declared, deductions and reliefs are properly claimed, and capital gains charges are correctly calculated.

Even small oversights can lead to penalties or paying more tax than necessary, so take a calm, methodical approach. If anything feels uncertain, seek professional guidance. Remember, the goal is not just to meet the deadline, but to submit a correct and complete return.