How to Amend a Self Assessment Tax Return After Filing It?

Filing your Self Assessment tax return can feel like a huge relief. Once you click submit, it’s tempting to assume everything is done and forget about it until next year.

However, mistakes happen. You might notice missing income, incorrect expenses, or even discover new information after filing.

The good news is that HMRC allows you to amend your Self Assessment tax return after submission.

This guide explains how to amend a Self Assessment tax return so you can avoid penalties, ensure you pay the correct tax, and keep your records accurate.

Key points

• Missing income and expenses are the most common reasons for amendment 📅
  Many taxpayers discover forgotten freelance income, unclaimed expenses, or incorrect figures after filing, all of which can affect the amount of tax they owe.
• Amending your return online is the fastest and easiest option 🖥️
  You can log into your HMRC account, select the relevant tax year, update the incorrect sections, and submit the amendment, with HMRC automatically recalculating your tax position.
• You still have options if you miss the amendment deadline ✔️
  If you miss the amendment deadline, you may still be eligible for a refund under overpayment relief. This allows you to recover overpaid tax, but the process is more formal, requires supporting evidence, and must usually be submitted within four years of the tax year.

Can you amend a Self Assessment tax return after filing?

Yes, HMRC allows you to amend your Self Assessment tax return after filing it. In fact, they expect taxpayers to correct errors as soon as they become aware of them.

You can amend your return if you:

• Forgot to include income
• Included incorrect income figures
• Missed allowable expenses
• Entered incorrect personal information
• Received updated documents after submitting
• Discovered accounting errors

Amending your return ensures your tax calculation is accurate. This can either increase or decrease your tax bill, depending on the correction.

If your amendment shows you owe more tax, you should pay the difference as soon as possible to minimise interest charges. If it shows you overpaid, HMRC will issue a refund.

Deadline for amending a Self Assessment tax return

You have 12 months from the original filing deadline to amend your Self Assessment tax return.

For example:

• 2023–24 tax year deadline: 31 January 2025
• Amendment deadline: 31 January 2026

This gives you plenty of time to review your return and make corrections if needed.

What if you miss the amendment deadline?

If you miss the amendment window, you can no longer correct the return through the standard online process. However, you may still be able to make an overpayment relief claim.

Overpayment relief allows you to request a refund if you believe you paid too much tax due to an error in your original return. This is most commonly used when:

• You forgot to claim allowable expenses
• You missed tax reliefs, such as pension contributions or Gift Aid
• You included incorrect income figures that resulted in overpaying tax
• You later discovered accounting errors

Unlike a standard amendment, overpayment relief is a formal claim. You must contact HMRC directly and provide detailed information, including:

• The tax year involved
• The amount you believe you overpaid
• The reason for the error
• Evidence supporting your claim

In most cases, you must submit an overpayment relief claim within four years of the end of the relevant tax year.

The process can take longer than a normal amendment, and HMRC may request additional documentation before approving your claim.

Common reasons people amend their tax return

Amending a Self Assessment tax return is more common than many people realise.

Even careful taxpayers can miss information, especially if they manage multiple income sources, rely on manual records, or receive documents late. Freelancers, sole traders, landlords, and company directors are particularly likely to need amendments, because their income and expenses aren’t always finalised at the time of filing.

Here are the most common reasons taxpayers amend their returns:

1. Forgotten income

Forgetting to include income is easy if you have multiple clients, bank accounts, or income streams. Sometimes income is missed because payments were received late, recorded incorrectly, or overlooked entirely.

Common examples include:

• Freelance or self employment payments received near the end of the tax year
• Bank interest from savings accounts
• Dividend income from shares or investments
• Rental income from property
• Side income from part-time work, consulting, or online platforms

Leaving income out can result in underpaying tax, and HMRC may charge interest or penalties if the omission isn’t corrected.

2. Missing or incorrect expenses

Expenses reduce your taxable profit, which directly lowers the amount of tax you owe. If you forget to include allowable expenses, you may end up paying more tax than necessary.

Commonly missed expenses include:

• Equipment, such as laptops, phones, or tools
• Software subscriptions used for business
• Office expenses, including stationery and supplies
• Travel costs, such as train fares, fuel, or parking for business trips
• Professional fees, including accountants, legal services, or subscriptions
• Home office expenses, if you work from home

In some cases, expenses may have been included but recorded incorrectly, either under the wrong category or with inaccurate totals. Amending your return allows you to claim the full range of allowable expenses, ensuring your tax bill reflects your true profit.

3. Incorrect figures or calculation errors

Manual errors are another common reason for amendments. These mistakes often occur when taxpayers rely on spreadsheets, handwritten records, or manual calculations.

Typical errors include:

• Entering incorrect income or expense totals
• Transposing numbers, such as typing £5,200 instead of £2,500
• Misreading bank statements or financial reports
• Entering gross amounts instead of net amounts, or vice versa
• Including or excluding VAT incorrectly

4. Receiving documents after filing

In some cases, you may submit your tax return before receiving all relevant financial documents. This is especially common if you choose to file early in order to avoid the January deadline rush.

Examples of late documents include:

• Annual bank interest summaries
• Dividend vouchers or investment statements
• Corrected or delayed invoices
• Updated bookkeeping records
• Final expense totals from accountants or accounting software

Once you receive this information, you may need to amend your return to reflect the correct figures.

5. Claiming reliefs or allowances you initially missed

Tax reliefs and allowances can significantly reduce your tax liability. Sometimes taxpayers realise after filing that they were eligible for relief they didn’t claim.

Common examples include:

• Pension contributions eligible for tax relief
• Gift Aid donations to charities
• Business expenses not originally included
• Marriage Allowance adjustments
• Loss relief from previous years

Reviewing your eligibility carefully can help ensure you benefit from all available reliefs, and adding these claims through an amendment may reduce your tax bill and result in a refund.

6. Changes to personal or business information

You may also need to amend your return if personal or business details were incorrect or incomplete.

Examples include:

• Incorrect employment details
• Changes to self employment income figures
• Updated property income information
• Corrections to partnership income
• Amendments to accounting periods

How to amend a Self Assessment tax return

The quickest and easiest way to amend your Self Assessment tax return is through your HMRC online account. Online amendments are processed faster than paper corrections, and HMRC automatically recalculates your tax bill.

Here are the steps you need to take:

Step 1: Sign in to your HMRC online account

Go to the HMRC Self Assessment service and log in using your Government Gateway ID and password. Once logged in, you will see your Self Assessment dashboard.

Step 2: Access your submitted tax return

From your dashboard:

• Select ‘Self Assessment’
• Click ‘More Self Assessment details’
• Select ‘At a glance’
• Choose the relevant tax year you want to amend

This will open the previously submitted return.

Step 3: Select the option to amend the return

Click ‘Amend return’. You will then be able to update the relevant sections, including:

• self employment income
• Business expenses
• Employment income
• Property income
• Interest and dividends
• Pension contributions
• Tax relief claims

You don’t need to redo the entire return. You can amend only the sections that require correction.

Step 4: Update the incorrect information

Carefully enter the corrected figures. Make sure you:

• Use accurate totals
• Check your records before entering new figures
• Ensure all income and expenses are complete

Step 5: Review the amended return

Before submitting, review your entire return to ensure:

• All figures are correct
• Nothing has been missed
• Reliefs and allowances are properly included

HMRC will show an updated tax calculation based on your changes.

Step 6: Submit the amended return

Once you are satisfied, submit the amendment.

HMRC will immediately update your tax calculation, and your account will reflect the revised amount owed or refunded.

You can amend your return multiple times within the amendment deadline if further corrections are needed.

How to amend a paper tax return

If you originally submitted your Self Assessment return on paper, you can still amend it.

You have two options:

Option 1: Amend your return online

Even if you originally filed by post, you can create an online HMRC account and amend your return digitally.

This option is recommended because:

• It’s faster
• Your tax calculation updates immediately
• It reduces processing delays
• Most taxpayers find online amendments much easier to manage

Option 2: Amend your return by post

If you prefer, you can write to HMRC with the corrected information.

Your letter should include:

• Your full name
• Your Unique Taxpayer Reference (UTR)
• The tax year being amended
• The specific sections being corrected
• The original figures
• The corrected figures
• A clear explanation of the changes

Send your letter to the HMRC address for Self Assessment enquiries. HMRC will review your corrections and update your tax record manually.

Keep in mind that postal amendments can take longer to process than online changes.

What happens after you amend your tax return?

After submitting an amendment, HMRC recalculates your tax position based on the updated information.

There are three possible outcomes:

1. You owe additional tax

If your amendment shows that you underpaid tax, you’ll need to pay the difference.

You should pay the additional amount as soon as possible. Paying promptly helps minimise interest charges and ensures your account remains in good standing.

2. You are owed a refund

If your amendment reduces your tax liability, HMRC will issue a refund. Refunds are typically paid directly to your bank account if your bank details are registered with HMRC.

The timing of refunds varies, but online amendments are usually processed faster than postal corrections.

3. Your tax position stays the same

In some cases, amendments don’t significantly change your tax liability. Even if there is no financial impact, updating your return ensures your records remain accurate and compliant.

How Making Tax Digital affects amendments

Making Tax Digital (MTD) is transforming how Self Assessment works, with the goal of improving accuracy and reducing errors.

Under MTD for Income Tax, eligible taxpayers will be required to:

• Keep digital records of income and expenses using compatible software
• Submit quarterly updates to HMRC throughout the year
• Submit a final declaration confirming their overall tax position

Because financial information is recorded and reported regularly, errors are more likely to be identified and corrected sooner.

This reduces the likelihood of major amendments after submission.

Even if you need to amend, using MTD-compatible software also makes this much easier, because your records are stored digitally, updated continuously, and readily accessible.

How ANNA makes tax return amendments easier

Many amendments happen because of disorganised records, manual tracking, or incomplete financial information. When you rely on spreadsheets, receipts, and separate bank accounts, it becomes easy to miss transactions or enter incorrect figures.

ANNA eliminates these problems by automating your financial records from the start.

ANNA combines your business account, bookkeeping, invoicing, and tax tools in one place. This means your financial data is recorded automatically as you work, without requiring manual input or complex setup.

ANNA can:

• Automatically capture and categorise expenses, ensuring every transaction is recorded correctly and every allowable expense is claimed
• Provide real-time tax estimates, showing exactly how much you owe HMRC at any time
• Automatically set aside tax with smart money pots, helping you stay prepared and avoid unexpected tax bills
• Create, send, and track invoices automatically, with payments matched to your records
• Offer a built-in UK business account, with cards, transfers, and full visibility in one place
• Automatically calculate and file VAT returns, keeping you compliant with Making Tax Digital requirements
• Automatically calculate and prepare Self Assessment filings, using your real-time financial data
• Send automatic reminders, helping you avoid missed deadlines and penalties
• Provide 24/7 tax support, giving you expert answers whenever you need them

Most importantly, ANNA offers a totally different experience from traditional accounting tools. You don’t need to learn complex software or rely on an accountant.

ANNA works seamlessly in the background, automatically managing your finances and tax records, so your Self Assessment is always accurate, up to date, and ready to submit or amend with confidence.

So, sign up with ANNA today, automate your taxes, stay compliant with HMRC, and file with confidence.