Forgotten or Undeclared Income Is One of the Most Common Reasons for an Amendment

Freelance work, a second job, rental income, dividends, savings interest, overseas income, and pension income are all easy to leave off a tax return by mistake. This happens most, for example, when someone has more than one source of income.

We can check your figures against your records and correct a tax return before a small error turns into a bigger problem. A forgotten source of income is a common error, not a red flag, and HMRC deals with cases like this every day. Anyone can have made a mistake somewhere along the way, and there is no charge just to find out whether you need to amend.

Missed Allowable Expenses Can Mean You Have Paid Too Much Tax

Business expenses, professional subscriptions, professional fees, mileage, working from home costs, and equipment or training costs often go unclaimed, so you end up paying HMRC more tax than you actually owe, and too much tax has already been paid, often because the return was filed in a rush before the deadline.

We go through your records for anything you may have missed, then amend your return so you are not left out of pocket. These are some of the simplest corrections to make, because you are usually entitled to claim the expense once it is added back into the tax return, and you can claim more than one missed expense in the same amendment. If the correct expenses were never filed in the first place, an amended tax return can bring your tax bill back down to the correct figure.

Incorrect Tax Reliefs Often Get Missed on a First Submission

Pension contributions, Gift Aid, professional subscriptions, employment-related expenses, Marriage Allowance, and loss relief are reliefs that get overlooked more than most, and each is a common reason clients come to us to amend a tax return.

If you missed a relief you were entitled to claim, we can check your original return and prepare the correct amendment. In some cases this means submitting an amended return rather than a fresh claim. In some cases you can claim relief going back further than the normal amendment window allows, no matter how long ago the original was filed. If you overpaid tax because a relief was missed, that money is still yours to claim back.

Employment Details Are Not Always Recorded Correctly the First Time

Multiple jobs, PAYE income, benefits in kind, redundancy payments, termination payments, and incorrect tax already deducted are areas where employment figures often end up wrong on a self assessment tax return, which are common mistakes on payroll-heavy returns.

We compare your payslips and P60s against what was filed, then correct any figures that do not match. A single payroll error can throw off several boxes on the same tax return, so we check the whole picture. We also confirm your assessment details are correct before closing the case. These corrections are usually quick once we have the paperwork.

Property Income Mistakes Are Common on a Self Assessment Return

Rental income, missed allowable expenses, jointly owned properties, mortgage interest treatment, and property sales each come with their own rules.

We also help with rental income left off a previous tax return by accident, going back over previous tax returns to check nothing else was missed. For example, a landlord with two properties might need more than one correction in the same tax return. If HMRC asks you to re-file a section of an older return, we handle that paperwork too.

Capital Gains Tax Errors Need a Careful Correction

Property sales, shares, cryptocurrency, business assets, and more than one disposal in the same tax year can all lead to a Capital Gains Tax figure that is wrong. Unreported losses are just as common, and they can reduce a tax bill when they are recorded correctly, so it pays to catch the error early.

An error here can affect the following tax year too, not just the one you are correcting. These corrections often take longer than a simple income correction, because more than one figure needs checking.

Here is roughly what happens once you contact Vexo Accounting to amend your tax return, and this page covers the process in the order it usually happens.

• We review your original tax return, your Unique Taxpayer Reference, and the records behind the figures
• We recalculate your tax position, correct the figures that are wrong, and explain what has changed and why
• We submit the amendment to HMRC, online or on paper, complete any supporting documents, and handle any follow-up letters

Most straightforward amendments can be submitted online, though a paper tax return sometimes needs a paper amendment, and older returns may need to be refiled by post. Simple corrections are usually the fastest to agree with HMRC, especially when filed well before the deadline.

Once the amendment has been submitted and processed, you can view statements and check your self assessment tax account online to confirm everything has updated correctly. We put our findings in writing before we submit anything, so you can read through the changes before we complete the process on your behalf. Once HMRC accepts the amended return, you will see the update in your online account. We also confirm the date the correction was filed and update your self assessment account so your records stay correct going forward.

For anyone who would rather re-file a paper return than go through us online, we can still help prepare it. A paper return takes slightly longer to process than an online one. You will also get a short letter confirming everything once HMRC has replied.

Timing matters when you correct a self assessment tax return, and these are the main time limits to keep in mind.

• You normally have 12 months after the self assessment filing deadline to amend a tax return
• For the 2024 to 25 tax year, the normal amendment deadline is 31 January 2027, in line with the standard filing deadline
• You generally need to wait 72 hours after filing online before you can submit an online amendment
• Overpayment relief may be available for up to 4 years after the end of the relevant tax year, where the conditions are met

The same rule applies whether you use HMRC's tax return online service or file on paper, and it is worth remembering if your self assessment tax return was filed close to the deadline. You can also check the status of a tax return online once HMRC has processed it. If a paper return needs correcting instead, we can re-file it directly with HMRC once the paperwork is ready. You can check your tax return options at any point by logging into your account, or by asking us.

We can talk you through your tax return options before the filing deadline for the following tax year arrives. For example, if the 31 January filing deadline for one tax year has passed, that does not affect your right to amend a different, earlier tax year within its own time limits. For older tax years outside the normal amendment window, overpayment relief is often the only route left, and these are corrections we handle often, especially if the error was only spotted recently.

The UK's estimated self assessment tax gap was £14.6 billion in 2024 to 25, against an estimated total self assessment tax liability of £76.9 billion for the same year. The UK's overall estimated tax gap across all types of tax was £59.2 billion in 2024 to 25, and HMRC's compliance activity generated an estimated £50.2 billion in compliance yield during 2025 to 26.

HMRC processes a huge number of corrections every year, and most start with a simple error on an otherwise well-filed tax return, a single missed dividend figure being a common example. Missing a deadline or a figure is rarely deliberate, which is why HMRC allows a set window to put things right, so missing a deadline does not have to end badly.

April 2026 alone saw 737,891 self assessment tax returns filed, showing how many people deal with their tax affairs outside the usual January rush. A late tax return can also bring an initial £100 penalty, with further penalties potentially added on top, and you can pay more tax overall once penalties and interest are added.

If you think a mistake has been made on your self assessment tax return, get in touch with Vexo Accounting today. We will review your situation and give you a free quote to amend a tax return, with no obligation to go ahead, whether the correction shows additional tax is due or a refund is owed to you. Ready to amend? Some clients want to amend straight away, others just want to check first.

Contact us now and let our team take the stress out of correcting your tax return, from your first phone call right through to the letter confirming HMRC has accepted the correct amendment, whenever it was originally filed. One overlooked error can sit on your record for years if nobody checks it, so get in touch before it becomes a bigger problem.