Self Assessment season comes around every year, yet thousands of people still make avoidable mistakes when completing their tax return. These errors can lead to delays, penalties, or paying more tax than necessary. Whether you’re a sole trader, landlord, or small business owner, understanding the common pitfalls can save you time, stress, and money.
Below are the most frequent mistakes people make, along with simple tips to avoid them.
1. Missing the Deadline
One of the most common mistakes is simply leaving it too late. The Self Assessment deadlines are:
- 31st October – paper returns
- 31st January – online returns and tax payment
How to avoid this:
Start gathering your records early and aim to file your return well before January. If you use an accountant, getting your information in early helps ensure everything is completed accurately and without the January rush.
2. Not Keeping Proper Records
Self Assessment relies heavily on accurate record keeping. Missing receipts or incomplete bookkeeping leads to errors or missed expense claims.
How to avoid this:
Keep digital records throughout the year. Use accounting software, apps for capturing receipts, and keep a clear log of income, expenses, and business mileage. HMRC may ask for evidence, so well organised records are essential.
3. Claiming the Wrong Expenses
Some people claim too little because they’re unsure what they’re allowed, while others mistakenly claim personal expenses or items that aren’t permitted.
How to avoid this:
Make sure you understand the rules around allowable expenses. Common examples include travel for business, office supplies, mileage, and a proportion of home working costs. If in doubt, speak to an accountant to ensure you’re claiming everything you’re entitled to – no more, no less.
4. Forgetting Additional Income
Forget to include something and HMRC will spot it eventually. Commonly missed income includes:
- Bank interest
- Dividends
- Income from property
- Foreign income
- Casual or side gig earnings
How to avoid this:
Create a checklist at the start of each tax year. Your accountant can help ensure nothing is missed.
5. Not Making Payments on Account
Many taxpayers misunderstand payments on account. These are advance payments towards next year’s tax bill. Missing them or not budgeting for them can cause cash flow headaches.
How to avoid this:
Check your tax calculation carefully. If payments on account apply, set money aside throughout the year so you’re prepared.
6. Entering Incorrect Figures
Typos, duplicated entries, or misreading bank statements can lead to errors that affect your tax. Even small mistakes can trigger HMRC enquiries.
How to avoid this:
Double check everything before submitting. Compare totals against your bookkeeping software or bank statements. If an accountant prepares your return, ensure you review the figures before approving.
7. Not Claiming Eligible Allowances and Reliefs
Many people miss out on legitimate savings including:
- Trading allowance
- Property allowance
- Marriage Allowance
- Capital allowances
- Pension contributions relief
How to avoid this:
Take time to understand what you’re entitled to. An accountant can help ensure you don’t leave money on the table.
8. Ignoring HMRC Notices or Letters
HMRC might request more information or clarify something. Ignoring these can lead to penalties or assessments based on HMRC’s own estimates.
How to avoid this:
Open and act on any HMRC correspondence. If you’re unsure what something means, ask your accountant before responding.
Final Thoughts
Self Assessment doesn’t have to be stressful. With good organisation, accurate records, and an understanding of what HMRC expects, you can avoid the most common mistakes. If you’re uncertain or simply want peace of mind, working with an accountant ensures your return is submitted correctly and on time – saving you stress and potentially tax too.
If you’d like support with your Self Assessment, I’m always happy to help.