Avoid penalties, stress, and last-minute errors—learn the most common Self Assessment mistakes UK taxpayers make and how to get it right every time.
???? 1. Missing the Deadline
How to Avoid It:
- Set reminders in your calendar to stay on track.
- If it’s your first time, register early with HMRC.
- Work with an accountant well before the January rush.
???? 2. Not Registering in Time
If it’s your first submission, be sure to register with HMRC by 5 October after the tax year ends.
How to Avoid It:
- Visit HMRC’s Self Assessment registration page and get your Unique Taxpayer Reference (UTR) number as soon as possible.
???? 3. Forgetting to Declare All Income
Remember to declare all sources of income, which includes:
- Rental income
- Dividends
- Freelance or side hustle earnings
- Overseas income
How to Avoid It:
- Keep a continuous record throughout the year. Utilize cloud accounting tools or apps to log every income source, even the smaller amounts.
???? 4. Claiming Incorrect Expenses
Claiming expenses that aren’t eligible can lead to penalties from HMRC, while under-claiming means missing out on tax relief.
How to Avoid It:
- Ensure your claims are “wholly and exclusively” for business purposes. Typical valid expenses encompass office costs, travel, software, and professional services.
❌ 5. Forgetting to Pay What You Owe
Remember, filing your return is just one part of the process—you also need to pay your tax bill by 31 January.
How to Avoid It:
- Double-check what you owe through your HMRC account and make payments via card or bank transfer. If needed, consider setting up a payment plan.
???? 6. Using the Wrong UTR or NI Number
Just one incorrect digit can delay your return or result in mismatches with HMRC.
How to Avoid It:
- Double-check both your UTR and National Insurance numbers before submission to ensure they match exactly with HMRC records.
???? 7. Doing It All Yourself Without Advice
Mistakes often happen when individuals try to navigate the return process or rely on outdated information.
How to Avoid It:
- Engage an accountant to review your return—or, even better, let them manage the whole thing for you.
???? Let Melon Make It Simple
At Melon Accountants, we simplify the Self Assessment process for you. We’ll:
File on time and without errors
Ensure you’re registered
Collect all your records
Maximize your deductions
