Can I Change My Tax Return After Submitting It

At Towerstone Accountants we provide specialist personal tax services, for self employed, and individuals across the UK. This article has been written to explain Can I change my tax return after submitting it, in clear practical terms, so you understand how personal tax and Self Assessment rules apply in real situations. Our aim is to help you stay compliant, avoid costly mistakes, and make confident tax decisions.

This is a question I am asked every year, often after someone has already clicked submit and then spotted a mistake almost immediately. From my experience, this is completely normal. Tax returns are detailed, the rules are not always intuitive, and it is very easy to miss something or misunderstand how a figure should be entered.

The reassuring answer is yes, in most cases you can change your tax return after submitting it. HMRC fully expects genuine mistakes to happen and the Self Assessment system is designed to allow corrections. What matters is when you correct it, how you correct it, and whether you do so within the relevant time limits.

In this article, I will explain how changing a tax return works in the UK. I will cover when you can amend a return online, what happens if the deadline has passed, how HMRC treats increases and reductions in tax, and when a formal disclosure is required. Everything here is based on real UK rules and my day to day experience dealing with Self Assessment returns for individuals, sole traders, landlords, and company directors.

Why people need to change tax returns

I want to start by saying something important. Needing to change a tax return does not mean you have done anything wrong. The UK tax system is complex and even people who file returns every year can make genuine errors.

Some of the most common reasons I see for amendments include:

• Missing allowable expenses such as mileage, use of home, or professional fees

• Forgetting to include income from a second job, side business, or freelance work

• Misunderstanding how dividends, CIS deductions, or rental income should be reported

• Using estimated figures and later receiving final numbers

• Getting professional advice after filing and realising something was missed

• Entering figures incorrectly into the online system

From my experience, HMRC is far more concerned with whether you correct an error than with the fact that the error happened in the first place.

The two main ways to change a tax return

How you change a tax return depends largely on timing. There are two main routes, and it is important to understand which one applies to you.

Changing a tax return within the amendment window

If you submitted your tax return online, you usually have 12 months from the filing deadline to amend it. This is known as the amendment window.

For example:

• A 2023 to 2024 tax return has a filing deadline of 31 January 2025

• You can normally amend it online until 31 January 2026

Within this window, the process is relatively straightforward.

You log into your HMRC online account, access your submitted return, choose the option to amend it, update the figures, and resubmit. The amended return then replaces the original version.

From my experience, this is the cleanest and least stressful way to correct mistakes, and HMRC treats these amendments as routine.

What you can change within this period

During the amendment window, you can change almost any part of your tax return, including:

• Income figures from employment, self employment, or property

• Expenses and allowances

• Capital gains entries

• Student loan information

• High Income Child Benefit Charge details

• Pension contributions

• Gift Aid claims

You are not restricted to small corrections. Even if the amendment changes your tax position significantly, that is acceptable as long as the information is accurate and complete.

What happens after you amend your return

Once you submit an amended return, HMRC recalculates your tax automatically.

If the amendment increases your tax bill, the extra tax becomes payable. Interest may apply depending on how late the payment is, and payment is due as soon as possible.

If the amendment reduces your tax bill, HMRC will update your account and process a refund of any overpaid tax. In some cases, this happens automatically. In others, you may need to confirm bank details.

From my experience, refunds following amended returns usually take a few weeks, although this can be longer during busy periods.

Changing a tax return after the amendment window closes

If the 12 month amendment window has passed, you can no longer change the return directly online. However, that does not mean you are stuck with an incorrect return forever.

At this point, corrections are made through a formal claim or disclosure to HMRC.

This usually falls into one of two categories, overpayment relief claims or voluntary disclosures.

Overpayment relief claims explained

If you discover that you paid too much tax because your return was incorrect, you may be able to claim a refund using overpayment relief.

This applies where:

• The original tax return was wrong

• The mistake resulted in too much tax being paid

• You are still within the time limit to make a claim

The time limit is generally four years from the end of the relevant tax year.

For example, an error in the 2019 to 2020 tax return can usually be corrected up to 5 April 2024.

From my experience, these claims require clear explanations and supporting evidence. HMRC will not automatically accept a claim without understanding exactly what went wrong and why.

How overpayment relief works in practice

An overpayment relief claim must be made in writing, either through HMRC’s online services or by letter.

You must clearly set out:

• Which tax year the claim relates to

• What was incorrect in the original return

• How the figures should be corrected

• How much tax was overpaid

• A declaration that the claim is accurate to the best of your knowledge

Poorly explained claims are one of the most common reasons for delays, and in some cases, outright rejection. This is an area where professional help often saves a lot of time and stress.

What if the mistake means you underpaid tax

If correcting the return means you should have paid more tax, this becomes a voluntary disclosure.

From my experience, HMRC looks far more favourably on taxpayers who come forward themselves rather than waiting for an enquiry.

A voluntary disclosure should explain:

• What the mistake was

• Why it happened

• How much extra tax is due

• Whether interest or penalties may apply

Interest will almost always be charged, but penalties are often reduced significantly when the disclosure is voluntary and cooperative.

Penalties and how HMRC looks at mistakes

One of the biggest worries people have is penalties. I want to be clear about this, because there is a lot of misunderstanding around how HMRC approaches errors.

HMRC assesses penalties based on behaviour, not simply on the amount of tax involved.

Broadly speaking, errors are categorised as careless, deliberate, or deliberate and concealed.

Most amendments I deal with fall into the careless category, or attract no penalty at all. Genuine mistakes, corrected promptly and openly, are very rarely treated harshly.

Key points to takeaway

From my experience, changing a tax return after submitting it is a normal part of Self Assessment. The system allows for corrections because HMRC understands that mistakes happen.

What matters most is acting quickly, being honest, and following the correct process. Ignoring an error rarely ends well, but addressing it properly almost always leads to a manageable outcome.

If you are unsure whether you need to amend a return, or how to do it without causing further issues, getting advice early can save you time, money, and unnecessary worry.

You may also find our guidance on How do accountants help people who have missed previous returns, and How do I check if I am owed a tax refund, helpful when reviewing related personal tax questions. For a broader overview of Self Assessment deadlines, reporting, and obligations, you can visit our self assessment guidance hub.