Filing a Self Assessment tax return can feel stressful. Many people find it confusing. Many people leave it until the last minute. Many people make small errors that cause big problems later. But the good news is this: you can avoid most issues with the right help and the right steps.
In this guide, City Gates Accountants explains the most common self assessment mistakes and how you can avoid them.This blog is written to help anyone understand the process, even if you have never filed a tax return before.
What Is Self Assessment?
Self Assessment is a system used by HMRC for collecting income tax. Instead of your tax being taken automatically, you must report your income yourself. You must also report any profits, expenses, or other financial details.
People who usually need to file Self Assessment include:
- Self-employed workers
- Freelancers
- Contractors
- Business owners
- Landlords
- High-income earners
- People with multiple income sources
If you fall into any of these groups, you must file your tax return every year.
But many people struggle with the process. That is why so many self assessment mistakes happen.
Why Do People Make Mistakes?
There are many reasons:
- The rules feel complicated
- People forget deadlines
- People don’t understand what income to include
- Records are messy
- People try to file quickly at the last minute
Most mistakes are simple. But they can cause penalties. They can cause delays. They can cause stress. This blog will show how simple steps can help you avoid trouble.
1. Missing the Deadline
This is the most common of all self assessment mistakes. Many people leave their tax return until the last week. Then they rush. Then they panic. Then they miss the deadline.
The deadlines are:
- 31 October for paper returns
- 31 January for online returns
If you miss the deadline:
- You get a penalty
- You may face interest charges
- You may get additional fines if the delay continues
How to Avoid This
- Mark the deadline on your calendar
- Start early
- Collect your documents in advance
- Ask for help if you feel confused
City Gates Accountants can help you prepare early and submit on time.
2. Forgetting to Register for Self Assessment
Some people forget that they need to register. They start working as self-employed. They earn money. But they do not tell HMRC. This is a serious issue.
If you fail to register, HMRC may charge a penalty.
How to Avoid This
- Register as soon as you start earning self-employed income
- Do not wait until January
- Visit the HMRC website to complete the registration
- Ask an accountant for help if you are unsure
- Registering early makes the process easy.
3. Not Reporting All Income
One of the biggest self assessment mistakes is leaving out income. Some people forget side income. Some forget rental income. Some forget online income. Some forget foreign income.
HMRC expects you to declare:
- Business income
- Rental income
- Freelance income
- Investment income
- Savings interest
- Dividends
- Cryptocurrency gains
- Income from online platforms
If you fail to report income, HMRC may charge penalties.
How to Avoid This
- Keep a list of all money you earn
- Check bank statements
- Keep invoices
- Track payments throughout the year
- Use accounting software
- Ask City Gates Accountants to review your records
It is better to report everything to avoid problems later.
4. Claiming Incorrect Expenses
Expenses reduce your tax bill. But you must claim them correctly. Some people claim too many expenses. Others claim too few. Both are common self assessment mistakes.
Incorrect claims may lead to:
- Penalties
- Extra tax
- HMRC investigations
Examples of incorrect expense claims:
- Claiming personal expenses as business expenses
- Guessing expenses instead of using receipts
- Claiming items not allowed by HMRC
- Not claiming valid expenses because of confusion
How to Avoid This
- Keep all receipts
- Separate personal and business costs
- Learn which expenses are allowed
- Let an accountant check your expenses
- Use simple digital tools to track spending
City Gates Accountants can help you claim the right amount safely.
5. Poor Record Keeping
Many self assessment mistakes happen because records are messy. People lose receipts. People forget invoices. People mix personal and business money.
If your records are unclear, your tax return may be wrong. HMRC may also question your numbers.
How to Avoid This
- Keep all receipts
- Organize invoices
- Store documents safely
- Create simple folders
- Use apps to store digital copies
- Keep business and personal finances separate
- Good record-keeping saves time and reduces stress.
6. Forgetting Payments on Account
Payments on account confuse many people. These are advance payments toward next year’s tax. HMRC asks for payments on account if:
- You owe more than £1,000 in tax
- You did not have enough tax collected through PAYE
Many people forget they must pay in January and July. This leads to surprise bills and late payment penalties.
How to Avoid This
- Check if you need to make payments on account
- Plan for both payments
- Save money throughout the year
- Ask your accountant to calculate your tax early
City Gates Accountants can help you understand these payments clearly.
7. Not Updating Personal Information
Some people forget to update their details with HMRC. If you move house. If your address changes. If your name changes. If your business changes. You must update HMRC.
Not updating your details can cause:
- Missed letters
- Missed deadlines
- Penalties
- Delays
How to Avoid This
- Log in to your HMRC account
- Keep your information updated
- Check your letters and emails regularly
8. Filing Incorrect Figures
Many people estimate numbers. They guess their income. They round expenses. They “think” the amounts are right.
This leads to errors. And HMRC can spot incorrect numbers easily.
How to Avoid This
- Use real figures
- Track all income and expenses
- Use accounting software
- Keep your records up to date
- Ask for professional help
- An accountant can ensure everything is correct.
9. Forgetting About Allowances and Reliefs
Another important part of avoiding self assessment mistakes is understanding what reliefs and allowances you can use. Many people miss out on:
- Personal allowance
- Marriage allowance
- Trading allowance
- Property allowance
- Pension contributions
- Charity gift aid
Missing these may mean you pay more tax than necessary.
How to Avoid This
- Check what allowances apply to you
- Ask an accountant to calculate your tax
- Keep records of pension and charity payments
- Learn HMRC rules for your income type
City Gates Accountants can make sure you do not overpay.
10. Not Asking for Help
Self Assessment can feel confusing. Many rules change every year. Many forms look complicated. Many people feel overwhelmed. Yet many still try to do it alone.
This often leads to mistakes.
How to Avoid This
- Ask an accountant for help
- Let professionals handle your tax
- Get advice early
- Do not wait until the last minute
City Gates Accountants specializes in helping people avoid mistakes and reduce stress.
How City Gates Accountants Can Help You
City Gates Accountants can help you avoid all common self assessment mistakes by providing:
- Professional tax advice
- Accurate calculations
- Proper record checks
- Timely submissions
- Deadline reminders
- Stress-free filing
- Help with HMRC rules
- Support with expenses and income tracking
We make Self Assessment simple. We save you time. We reduce errors. We help you stay compliant.
Tips to Make Self Assessment Easy Every Year
Here are simple tips:
- Start early
- Keep good records
- Use accounting software
- Keep receipts safe
- Separate personal and business money
- Ask for help
- Review your return before submitting
- Stay organized all year
- Keep track of deadlines
- Save money for tax
- Understand basic HMRC rules
With these steps, filing your tax return becomes much easier.
Conclusion
Filing a Self Assessment does not have to be stressful. Most self assessment mistakes happen because people rush, guess numbers, or fail to plan. But with good records, early preparation, and simple guidance, you can avoid problems.
City Gates Accountants is here to help you every step of the way. With professional support, you can file your return correctly, avoid penalties, and save time.
Frequently Asked Questions ( FAQs )
What are the most common Self Assessment mistakes?
Missing deadlines, incorrect expenses, poor records, and forgetting income.
What happens if I miss the deadline?
You may receive penalties and interest charges.
Can I fix mistakes after submitting my tax return?
Yes. You can amend your return within 12 months.
Do I need an accountant?
You do not have to, but an accountant helps reduce errors and stress.
What is Payments on Account?
Advance payments toward next year’s tax bill.