Self Assessment error or mistake

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First, a UK tax Self Assessment error or mistake as a UK contracting professional can result in missing the HM Revenue & Customs (HMRC) tax return deadline (UK). Therefore, what happens if you make a mistake on your tax return (UK)? If we look at Self Assessment for directors, when there are Self Assessment errors and your tax return is incorrect, HMRC may impose a fine. Also, you must do this again when your limited company contractor Self Assessment (HMRC SA) return is wrong due to a tax return error the first time. This is because there’s an official requirement to correct tax return mistakes. Further, you may have to pay extra Self Assessment tax (UK) when you correct this. Therefore, if you don’t know what to do after making an HMRC Self Assessment mistake, there are some official HMRC errors and mistakes guidance to follow.

Most small business owners, be they sole traders, partners in a partnership, or UK contractors who are directors of a contracting limited company, must complete a Self Assessment (UK) Income Tax Return each year. If you’re a UK contractor, Self Assessment tax is one of your contractor taxes, albeit a personal tax rather than company tax. Therefore, when you complete your HMRC tax return, please don’t make a contractor SA error or tax return mistake. If you’ve made a mistake on Self Assessment return, you should ask an accountant for help or refer to HMRC errors and mistakes guidance.

This guide will consider what happens if Self Assessment is wrong and how to correct your contractor’s tax return. It is an excellent read on potential HMRC Self Assessment tax return form errors, especially if you’re completing your first-time Self Assessment tax return (UK).

Initial thoughts 

First thoughts

If you’re new to HMRC SA as a contractor limited company owner or for any other reason, you may wonder what is a Self Assessment tax return (HMRC). What’s more, when you’re required to file an SA tax return, you could do this yourself. On the other hand, you might consider looking for a UK Self Assessment tax return accountant near me to look after your tax affairs. However, if you plan to file your own SA, you should know how to complete a UK tax Self Assessment tax return form. More importantly, when you do this, you must ensure you don’t make an HMRC personal tax return mistake or an error on your tax return. Basically, if you discover my Self Assessment tax return is wrong and you’ve made tax return errors, you should consider how to correct these.

Requirement to file an HMRC tax return

As a UK individual, you must complete a personal tax return if you’re both:

  • You’ll have a personal tax bill in the current tax year.

Individuals are required to file a UK Self Assessment (HMRC SA) Tax Return every 12 months. Limited company contractors are directors of their own companies. Therefore, in most cases, they must complete an SA tax return each year.

When you file your HMRC Self Assessment form, besides reporting your taxable income and paying the tax you owe, you may be required to make payments on account in the future. If you have a good contractor accountant, they’ll help guide you through this process.

HMRC online personal tax account

Registering online for a Government Gateway user ID and password is a good idea. Nowadays, if you search for this, it will redirect you to the official HMRC sign-in page. Therefore, when you access this page, you can create the sign-in details for their digital service. As part of this process, you can register for an HMRC Self Assessment account (personal tax account) with HMRC.

With this in place, you can view your tax liabilities, payments, and due dates for each tax year. You can also view any tax owing and your PAYE coding notices. Therefore, you can check your latest tax code, and if there’s something in here that shouldn’t be, you or your accountant can contact HMRC and ask them to correct this.

Self Assessment error or mistake 

Initial SA considerations 

When required, an annual task is to file a UK tax return each year. The tax year covers 6 April to the following 5 April. Moreover, you must file your return with HMRC by the following 31 January after 5 April. Therefore, for the tax year ending 5 April 2024, the due date for filing your return and the HMRC Self Assessment payment is 31 January 2025. Likewise, for the tax year ending 5 April 2023, the due date for filing and payment was 31 January 2024.

Sad as it is, many people always leave this until the last minute. As a result, many may have a tax return problem after they have filed the form. Furthermore, UK Self Assessment errors can occur if you prepare this yourself without the help of an accountant. If your tax return is incorrect, you may pay more tax than is due.

File & check Self Assessment tax return (UK)

The best practice is to file your HMRC tax return (SA) early each year. We advise you to check through this from start to finish once it’s complete. When you do this, you can check you haven’t made a Self Assessment error or mistake. As a result, you’ll have peace of mind, knowing you’re fulfilling your duties correctly and on time.

Moreover, a tax return error or contractor mistakes can often arise if you don’t check your return before filing it. There are some common reasons for such errors, which we’ll show below.

Unique Taxpayer Reference (UTR) 

You must show your correct Self Assessment UTR number on your tax return and ensure your National Insurance number is correct. If you discover my National Insurance number or UTR is incorrect on your tax return, it’ll void this when you submit it.

As an individual, you’ll receive your NI number before you begin work in the UK. Indeed, when you’ve been working, your NI number will show on any previous payslips and tax documents you receive from HMRC.

Your UTR will show on last year’s tax return and any HMRC SA correspondence.

Self Assessment error or mistake (UK) -imprecise records

You must keep records of your income and any reliefs safe throughout the tax year.

To help avoid a tax return error or mistake, you should keep in a safe place the details of your:

  • Salary -this is shown on form P60 or form P45 and your payslips.
  • Dividends -from your own company and any others. Any company dividends from other companies should show on the dividend vouchers they send you.
  • Benefits in kind will show on form P11D. Benefits include company car benefits, medical insurance, beneficial loans, and others.
  • Bank interest on personal bank accounts. This doesn’t include ISAs.
  • Pension income -state pension or personal pension(s).
  • Government benefits include universal credit, employment, support allowance (ESA), and income support.
  • Rental property income details -include the total of your rental income and any related expenses.
  • Donations under Gift Aid.
  • Any personal pension contributions.
  • The details regarding Child Benefit received -if you receive this, you’ll receive thirteen four-weekly payments each year.
  • Payments into an employee share scheme.
  • Investments under Venture Capital Trust schemes, such as EIS.

Various Self Assessment error or mistake examples 

There are many examples of where you can make errors on your tax return. Filing your return with incorrect details will be a false Self Assessment tax return. Consequently, it’ll require correcting. Therefore, extra care and attention are required when you complete your tax return (SA), either by yourself or through your accountant. 

Miss the filing deadline 

A widespread HMRC Self Assessment mistake is missing the tax return deadline (UK), which is quite common. It’s more likely to occur if you leave the filing until close to the tax return deadline. Many accountants and tax experts are under pressure from some of their clients. This is because certain people will always send them their tax return information at the very last minute. When you prepare your return at the last minute, it may become apparent you haven’t included some information on this or something else is incomplete. This could lead to your inability to file your return on time.

If you’re completing a Self Assessment return via the HMRC website, please remember to save your return as you go along. After filling in all the sections and questions within those and completing Self Assessment to the end of the process, please ensure the return is sent online via their website. Once the online tax return (UK) has been completed, they’ll confirm receipt. 

How might you misreport your income as a contractor error in your tax return? 

Whoever will prepare your tax return, you or your accountant, please ensure you double-check the figures are correct. This can be another error in Self Assessment tax return if you don’t check everything and something on your return is incorrect. Basically, you must ensure you include all the figures for your income and reliefs. Income is typically salary, dividends and any other income. Reliefs are payments under Gift Aid, personal pension payments, and investments under Venture Capital Trust schemes such as EIS. If you miss including any of these, it’ll result in Self Assessment errors.

If your accountant prepares your return on your behalf, please ensure you check all the details are correct before signing off.

Self Assessment error or mistake -did you fail to declare all your income? 

You must include all your taxable income on your tax return. Your income will consist of both revenue and any Capital Gains. However, certain types of income you may receive aren’t taxable and including these results in an error on your tax return. These items include:

  • ISAs.
  • UK Government Gilts.
  • Premium Bonds.
  • Betting winnings.
  • Lottery winnings.

Self Assessment wrong -did you complete the wrong box or boxes?

There are many questions on a UK tax return and completing the wrong boxes is one of those mistakes to avoid. Therefore, you must be very careful when you complete the form so you don’t make a Self Assessment error or mistake. Usually, a business owner will let their accountant take care of their tax return. However, if you do this yourself and complete the wrong boxes, it’ll be a mistake in your Self Assessment tax return.

The tax return is wrong -did you forget to include supplementary pages? 

Another common mistake on Self Assessment (UK) is to overlook to include tax return supplementary pages with your return. Basically, you may have to submit extra pages with your return if you have other income. Indeed, these additional pages will include:

  • Interest from gilt-edged and other UK securities.
  • Life insurance gains.
  • Share schemes.
  • Employment lump sums or any compensation payments from a previous employer.
  • Stock dividends, non-qualifying distributions, and loans that you write off.

Mistake on tax return -did you forget to sign and date it? 

You may be one of the few who will still send your return through the post by 31 October. This date is three months earlier than the online filing deadline of 31 January. If you do this, please ensure you sign and date the declaration before you send it to HMRC. Overlooking to sign and date is another tax return error some will make when sending a paper tax return.

How can you amend Self Assessment tax return?

If you discover you’ve made an error on your tax return and filed an incorrect return, you can correct this. Basically, you can amend your tax return after submission (UK) by filing another tax return with the correct details.

What other SA aspects are there to consider?

HMRC guidance -Self Assessment error or mistake

If you make an error, HMRC has ways of checking certain types of income, such as employment income. Basically, if this occurs and they discover an error, they’ll send you a Tax Calculation to inform you what your new tax liability is.

The tax office has a web page covering HMRC errors and mistakes guidance. This covers various aspects of how you can change or amend your return. Indeed, it’s beneficial if you find you’ve made an HMRC Self Assessment mistake. Therefore, you can visit this page on HMRC errors and mistakes guidance, should the need arise.

If you’re completing your tax return online, HMRC has another guide that explains possible onscreen warning messages in unlikely situations. If you have an issue to resolve, HMRC’s customer forums could be a page to visit.

Paying Self Assessment tax bill

As an SA taxpayer, you must pay your tax bill each year. What’s more, you must pay the correct amount by the due date of 31 January, following the tax year-end. The reference to quote with your payment is your ten-digit HMRC SA UTR followed by a capital K. If you quote an incorrect reference, HMRC won’t be able to allocate the payment to your account. As a result, your payment will go astray. Therefore, quoting the correct reference with your online payment is important.

Incorrect Self Assessment penalties 

HMRC will charge penalties when there are mistakes on the tax returns. This includes late or inaccurate tax returns. Also, they charge penalties when a taxpayer pays the tax that’s due late. Therefore, it’s vital to make sure you get this right.

If you can’t pay your penalties or tax liabilities, you should contact HMRC Self Assessment by phone. Their usual phone number is 0300 200 3310, and the line is open Monday through Friday between 8 a.m. and 6 p.m.

Are you due overpayment relief? 

If you believe you’ve overpaid your income tax in a previous year, you must follow a specific process when you apply to HMRC for overpayment relief. This page on overpayment relief takes you to the HMRC guide, which provides more details regarding a tax refund. The overpayment relief option replaces the previous HMRC error or mistake claim rules.

Do HMRC make mistakes?

Occasionally, HMRC will make tax mistakes, too. Therefore, what to do if HMRC makes an error? If you discover an HMRC mistake on Self Assessment, you should contact them and advise them to correct this. Therefore, if HMRC made a mistake, you can call HMRC on 0300 200 3310 (the lines are open from Monday to Friday, 8 am to 6 pm). On the other hand, you can write to them about any HMRC mistakes; however, if you choose this method, it’ll take them longer to resolve the issue.

If you find you’ve registered for Self Assessment in error, once again, you can contact them. When you call or write, you can advise them to take you out of the HMRC SA system, as you’re not required to complete an SA return for the year in question.

Final thoughts 

Your UK Self Assessment tax return requires filing every 12 months. Indeed, a tax return error can occur if you or your accountant aren’t careful when you complete this. This guide covers various examples of a UK Self Assessment error or mistake which may arise and explains what to do if you make an error. If your return is wrong, there’s a requirement to correct this, and you can do so by filing an amended return with HMRC. Moreover, as mentioned earlier, you can refer to HMRC errors and mistakes guidance for further official Self Assessment advice. Finally, please ensure you give your tax return a detailed review before you or your accountant submit it to HMRC.

Link to Contractor Advice UK group on


Published On: April 6th, 2024 / Categories: Self-Assessment /

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