Amend Your MTD Quarterly Update After Submission: Step-by-Step

You've filed your quarterly update - and spotted a mistake. What now?

It happens to almost everyone at some point. You submit your Q1 MTD quarterly update, close the laptop, and then notice that you forgot to include £340 of broadband expenses, or you realise a chunk of income was put in the wrong category. The question is: can you fix it after submission, and if so, how?

The short answer is yes - you can amend a quarterly update after it has been submitted to HMRC. But the process is different from editing a draft before the deadline, and there are some things you need to understand before you start. This guide walks you through the amendment process step by step, explains the timelines involved, and covers the most common scenarios where sole traders and landlords need to correct a submitted update.

What "submitted" actually means in MTD

When you submit a quarterly update through MTD-compatible software, the figures are sent directly to HMRC's systems. Unlike a paper form you could retrieve from a post tray, a submitted update creates a record in HMRC's API (the technical connection between your software and HMRC). That record does not simply disappear if you want to change it.

However, MTD is designed to allow corrections. HMRC's quarterly updates are not treated as final tax assessments - they are periodic snapshots of your income and expenses. The figures are ultimately reconciled at your end-of-year final declaration, which is when your actual tax liability is calculated. This means that correcting a quarterly update, while important, does not immediately create or remove a tax bill on its own.

Understanding this reduces the panic. A mistake in your Q1 update is not the same as filing a fraudulent tax return. It is a figure that needs correcting, and HMRC's system accommodates that.

How the amendment process works

To correct a submitted quarterly update, you need to submit a replacement update for the same period through your MTD-compatible software. You cannot phone HMRC and ask them to change the numbers on your behalf - the correction must go through the software, using the same API connection that handled the original submission.

Here is what that process looks like in practice:

1. Log in to your MTD software and locate the quarterly update you need to amend. In AffordableMTD, this is shown in your submission history.
2. Open the relevant quarter - for example, Q1 covering 6 April to 5 July 2026.
3. Edit the figures that were wrong. This might mean adding a missed expense, removing a duplicate entry, correcting an income amount, or moving a figure to the correct category.
4. Review the updated totals carefully before resubmitting. Check that your corrected figures add up correctly across all income and expense categories.
5. Resubmit the update to HMRC. The software sends the corrected figures as a replacement for the original. HMRC's system stores the most recent version.

That replacement submission overwrites the earlier one in HMRC's records. You do not need to flag the amendment separately or write to HMRC to explain it - the process is handled automatically through the software API.

How many times can you amend a quarterly update?

There is no hard limit on how many times you can resubmit a quarterly update during the tax year. If you find a second error after correcting the first, you can submit another replacement. However, this should not become a habit - repeatedly correcting the same period's figures could attract attention if it results in large swings in your reported income or expenses.

The practical limit comes at the end of the tax year. Once you have submitted your final declaration for the year, your quarterly update figures are locked as part of that filing. At that point, any corrections would need to go through HMRC's standard amendment process for tax returns, which is a separate and more involved procedure.

Timelines: how quickly can you amend?

You can amend a submitted quarterly update at any point before you file your final declaration for that tax year. For the 2026-27 tax year, the final declaration deadline is 31 January 2028. That gives you a significant window.

In practice, it is worth correcting errors as soon as you spot them rather than leaving amendments until the end of the year. If HMRC's risk systems flag your records for a compliance check, having uncorrected errors sitting in your quarterly updates for months does not look good, even if you plan to fix them eventually.

There is also a practical reason to act quickly: the longer you leave it, the harder it becomes to reconstruct exactly what went wrong. Bank statements, receipts, and invoices are easier to find when the original transaction is recent.

Common scenarios where you might need to amend

Missed expenses

You submitted your Q1 update and then found a stack of receipts you had not entered - perhaps a software subscription, a broadband bill, or a professional fee you paid in April. This is one of the most common reasons people need to amend a submitted update.

To fix it, open the relevant quarter in your software, add the missing expenses to the correct categories, and resubmit. Make sure you have the receipts or records to support what you are adding - HMRC can ask for evidence of any expenses you claim, and your records need to be kept even if the submission has already gone in.

For guidance on which expenses belong in which category, see our posts on allowable expenses for sole traders and landlords and what counts as a landlord expense in your Q1 MTD quarterly update.

Miscategorised income

If you have both self-employment income and rental income, it is easy to put a figure in the wrong income source - especially if you are new to MTD. This matters because HMRC treats these income types differently for tax purposes. An amount entered under property income that should be under self-employment (or vice versa) will affect how your tax is calculated at the year end.

Correcting this involves reducing the figure in the wrong category and entering it correctly in the right one, then resubmitting. Our guide on mixed income MTD and which expenses count for self-employment vs property can help you work out where things should sit.

Incorrect amounts

A typo can make a significant difference - entering £2,500 instead of £250, for example, or forgetting a decimal point. If you spot an amount error, correct it in the relevant field and resubmit. Do not try to "cancel out" an incorrect figure by adding an offsetting entry in a different field. Simply correct the figure that was wrong and let the replacement submission do the rest.

Duplicate entries

Some people accidentally import expenses twice - once from a CSV file and once by manual entry. If your totals look higher than expected, check your expense list for duplicates before resubmitting. Our CSV upload and AI categorisation guide explains how to avoid this when importing expenses in bulk.

Income that should not have been included

Not every payment that lands in your bank account is taxable income for MTD purposes. If you included a personal transfer, a loan repayment from a friend, or a VAT refund as income, you would need to remove it from your quarterly update. See our guide on what income types MTD quarterly updates accept if you are unsure what should be included.

Will amending a quarterly update trigger a penalty?

Correcting an honest mistake in a submitted quarterly update does not itself trigger a penalty. HMRC's MTD penalty system focuses primarily on late submissions and late payments, not on amendments to figures within a submitted update.

The key distinction is intent. An amendment that corrects a genuine error is treated differently from a pattern of behaviour that looks like deliberate non-compliance. HMRC expects people to correct errors when they find them - that is partly why the amendment process exists.

Where penalties can become relevant is if the original error led to an underpayment of tax and you did not correct it. At the final declaration stage, if your declared income is materially lower than it should be because of an uncorrected quarterly update error, and HMRC identifies this during a compliance check, that could result in a penalty. The safest approach is always to correct errors promptly rather than leaving them to sort out later.

What HMRC sees when you amend

When you submit a corrected quarterly update, HMRC's system receives the replacement figures through the API. HMRC can see that a resubmission has been made - this is logged as part of your MTD record. However, submitting a correction is not unusual and does not in itself trigger a compliance check or investigation.

If you are concerned about a specific error - particularly one involving a significant amount of money or an income type that might look unusual - it is worth keeping a note of why you made the correction and what evidence supports the amended figures. If HMRC ever does ask about your records, you want to be able to explain the correction clearly. See our post on preparing records for HMRC enquiries after your Q1 MTD filing for more on this.

What if the error affects your payment on account?

MTD quarterly updates do not directly trigger payments on account in the way that a tax return does. Your payments on account are based on your previous year's tax liability and are not recalculated every time you submit or amend a quarterly update. So correcting a quarterly update will not immediately change what you owe HMRC right now.

The correction will, however, feed into the accurate figures that your final declaration is based on at the end of the tax year - and that is what ultimately determines your tax liability. For more background on how quarterly updates and payments on account relate to each other, see our post on MTD quarterly updates vs payments on account.

If you use bridging software: what the process looks like

If you use bridging software like AffordableMTD, you submit your quarterly updates by entering (or importing) your figures and then pushing them to HMRC through the software's connection. Amending a submitted update follows the same basic steps: go back to the quarter, correct the figures, and resubmit.

Bridging software works by taking the figures you provide and sending them to HMRC - it does not keep a running ledger of every transaction in the way that full accounting platforms aimed at larger businesses might. This means you need to make sure your own records (spreadsheets, receipts, bank statements) match whatever you are submitting, both in the original update and in any amendment. Your records are the source of truth - the software is the means of sending them to HMRC.

If you are not sure your records are in good shape before amending, our post on Q1 MTD record fixes covers how to get them straight.

Step-by-step summary for amending a submitted quarterly update

1. Identify exactly what was wrong - which figure, which category, and what the correct amount should be.
2. Gather the supporting evidence - receipt, invoice, bank statement - before you start editing.
3. Log in to your MTD software and open the relevant quarterly period.
4. Make the correction directly in the relevant field. Do not try to offset errors with other entries.
5. Check the updated totals make sense before resubmitting.
6. Submit the corrected update to HMRC. Keep a note of when you submitted and what you changed.
7. Update your own records so they match what you have submitted.

Wrapping up

Spotting an error in a submitted quarterly update is frustrating, but it is not a crisis. The MTD system is designed to allow corrections, and submitting a replacement update with the right figures is a straightforward process. The important things are to act quickly, correct only what is genuinely wrong, keep your supporting records in order, and make sure your corrected submission reflects what actually happened in that quarter. Do that, and you are in a good position heading towards your end-of-year final declaration.