Amending MTD Submissions: Step-by-Step Guide to Corrections and Timelines

Introduction — why prompt corrections matter under MTD ITSA

Making Tax Digital for Income Tax Self Assessment (MTD ITSA) changes how sole traders, landlords and many self-employed people report income to HMRC. The new system uses quarterly updates, an end-of-period statement (EOPS) and a final declaration. With quarterly reporting, errors can appear sooner — and fixing them quickly keeps your tax right, reduces interest and avoids penalties.

Who this guide is for and the 2026–2028 rollout

This practical, step-by-step guide explains how to amend mistakes in MTD submissions and what timelines to expect during the staged rollout:

• April 2026 — businesses with income over £50,000 must comply
• April 2027 — income threshold reduces to over £30,000
• April 2028 — income threshold reduces to over £20,000

We explain how to correct errors in quarterly updates, the EOPS and final declaration, how to handle corrections for past tax years and how commercial software fits into the process.

Important note for Limited Companies

If you run a limited company: MTD for Corporation Tax is not mandated for 2026 (estimates remain 2028+). However, from March 2026 you must use commercial software to file CT600 corporation tax returns. This article focuses on MTD for Income Tax (ITSA) for self-employed people, partnerships and landlords.

Step 1 — find and classify the error

First, be clear about what happened. Most mistakes fall into one of these groups:

• Transposition or typing error (e.g. £12,350 recorded as £1,235)
• Misallocated expense (e.g. a personal cost recorded as business)
• Duplicate income or missing income
• Incorrect accounting period or VAT basis applied to figures
• Late discovery of earlier-year errors

For {industry} businesses, common cost categories to check include equipment purchases, travel and subsistence, tools and vehicle expenses. For landlords, double-check mortgage interest, repairs, letting agent fees and council tax recharges.

Step 2 — check whether you can fix it in your next quarterly update

One of the advantages of MTD’s quarterly updates is that many small mistakes can be corrected in a subsequent filing rather than by a formal amendment to a past year. Use this approach when:

• The error affects the current tax year and you haven’t submitted the final declaration yet.
• The correction is straightforward: add or subtract the difference in the relevant income or expense box on your next quarterly update.

That approach keeps the digital trail intact and is quick. Make sure you record an explanation in your accounting software notes so you can show why the change was made.

Step 3 — amending the EOPS or final declaration

If you discover an error after submitting an EOPS or the final declaration, you must use your MTD-compatible software to make an amendment. The usual steps are:

• Open the original period in your accounting software.
• Make the correction against the specific income or expense item.
• Resubmit the corrected EOPS or final declaration (software will often label this as an amendment).
• Save the audit trail and any explanatory notes for your records.

Your software will communicate digitally with HMRC. Do not try to correct the paper Self Assessment return or send spreadsheets — the change must be made through MTD-compliant software.

Step 4 — correcting mistakes from an earlier tax year

For errors in previous tax years, the approach depends on whether the earlier year has already been taxed and whether the statutory amendment window remains open:

• If the year is still within HMRC’s amendment window, you can make a formal amendment. For Self Assessment returns this is often available for 12 months after the statutory filing deadline (check the current HMRC rules for exact periods).
• If the amendment window has closed, you may need to disclose the error to HMRC voluntarily using their formal disclosure process. Early, full disclosure usually reduces penalties.

Because MTD ITSA changes the submission route, you will normally use your MTD software to make the amendment or to prepare the disclosure. If you are unsure, contact your accountant or HMRC’s specialist helpline for guidance before filing.

Step 5 — timelines and practical deadlines

Practical timelines to keep in mind:

• Correct small current-year mistakes immediately in your next quarterly update — don’t wait. The sooner the correction appears in digital records, the easier it is to explain and the less likely interest will accrue.
• Amend EOPS or final declarations as soon as you discover the error. Software allows resubmission; aim to act within days not months.
• For earlier tax years, check the statutory amendment period (often 12 months from the filing deadline) and act within that window where possible.
• If you owe extra tax because of the correction, pay the tax promptly to reduce interest and potential penalties.

Remember the staged rollout dates: if you cross the income thresholds in April 2026/27/28, you must already be using MTD-compatible software to meet reporting and amendment requirements.

Step 6 — keep a clear digital audit trail

HMRC expects digital record-keeping. Your software should:

• Keep an unalterable audit trail showing the original figure and the correction
• Allow you to record a short note explaining why you corrected the figure
• Store invoices, receipts and bank records digitally for at least six years (longer if relevant)

Do not delete or overwrite original entries. Instead, make correcting entries so you can demonstrate the chain of events if HMRC queries the return.

Step 7 — what to do if the correction increases tax due

If the correction means you owe more tax:

• Pay as soon as you can to limit interest and penalties.
• If payment in full would cause genuine hardship, contact HMRC and explain your situation — they may offer a Time to Pay arrangement.
• When telling HMRC about an underpayment, be factual and supply supporting figures produced by your software. Voluntary disclosure and early payment usually reduce penalties.

Penalties, interest and reasonable care

HMRC charges interest on unpaid tax from the date it was due. Penalties for inaccuracies depend on whether the behaviour was deliberate, careless or accidental, and whether you took reasonable care. Correcting mistakes quickly and keeping clear records demonstrates reasonable care and will usually limit penalties.

Using software to amend — practical checklist

• Ensure your accounting software is MTD-compatible and updated.
• Locate the original quarterly update, EOPS or final declaration in the software.
• Enter the correction with a concise explanation in the notes field.
• Resubmit the period as an amendment — follow the software prompts.
• Download and store the confirmation from HMRC and the software’s audit log.

Common scenarios and sample fixes

Scenario: You recorded a new tool purchase for £1,200 as £120 in February, after the Q2 submission. Fix: Enter the correct £1,200 in the next quarter using a correcting entry, add a note referencing the original mistake and resubmit EOPS when the year end comes. If the mistake created a material change to tax due for the previous quarter, amend that quarter’s submission in your software.

Scenario: A landlord missed rental income from an overseas tenant two years ago and the amendment window has closed. Fix: Consider a voluntary disclosure to HMRC with the help of your accountant. Be ready to show receipts, bank statements and the corrected figures from your MTD software.

Voluntary disclosure and ‘reasonable excuse’

If you find a significant historical mistake and you cannot correct it through the normal amendment window, voluntary disclosure is the best route. Be candid: supply corrected figures, supporting documents and an explanation of what happened. Full disclosure generally reduces penalties. ‘Reasonable excuse’ is narrow and applies where events outside your control prevented compliance — it is not a routine defence for bookkeeping errors.

Record retention and supporting evidence

Keep a clear digital backup of all supporting evidence, including:

• Invoices and receipts
• Bank statements
• Purchase orders and contracts
• Notes in software explaining corrections

HMRC normally advises retaining business records for at least six years. For matters involving amendments and disputes, keep them until any inquiry or settlement is final.

Practical tips to reduce future mistakes

• Use MTD-compatible bookkeeping software, and keep it up to date.
• Reconcile bank accounts monthly, not just at year end.
• Create a simple process for recording receipts immediately, including photos saved in your software.
• Segregate personal and business spending, especially when using a personal card for business costs.
• Get professional review at least twice a year — a relaxed mid-year check greatly reduces EOPS pressure.

Who to contact if you’re unsure

If you are unsure how to proceed, you have options:

• Contact your accountant or tax adviser — they can help prepare amended filings and manage dialogue with HMRC.
• Use HMRC’s MTD help pages and helplines for technical queries about digital submissions.
• If you use software support, ask the provider how to perform an amendment — many have step-by-step guides for corrections and audit logs.

FAQs — short answers

• Can I just file a nil quarterly update and fix everything at year end? No. Quarterly updates must reflect the period’s activity. Deliberately filing nil returns to delay corrections is risky and may attract enquiry. Small adjustments may be made in later quarters, but be transparent in your notes.
• Do I need to contact HMRC each time I amend? Not usually — your MTD software communicates the amendment. Contact HMRC if the amendment creates a significant underpayment or you need to arrange payment terms.
• Will correcting mistakes stop HMRC penalties? Not automatically. Early correction and disclosure reduce penalties and support a reasonable care defence, but interest on unpaid tax still applies.

Final thoughts — making corrections straightforward

MTD ITSA’s quarterly rhythms make it easier to catch and correct mistakes sooner. Use MTD-compatible software, keep your records clear and act quickly when you spot an error. If you’re unsure, professional advice helps you choose between correcting in the next quarterly update, amending an EOPS/final declaration, or making a formal disclosure to HMRC. We’re here to help you make tax digital — and to make staying compliant as simple and stress-free as possible.

If you’d like support reviewing corrections or selecting software that makes amendments straightforward, get in touch — we’ll guide you step by step.