Tax Return Amendment Deadlines and Remedies: 2026/27

Section 9ZA of the Taxes Management Act 1970 (TMA 1970) provides the primary statutory mechanism for amending a submitted tax return for individuals and trustees. Taxpayers may amend their personal or trustee tax return simply by giving notice to an officer of the Board.

For corporate entities, Schedule 18, Paragraph 15 of the Finance Act 1998 establishes a parallel right. Companies can amend their company tax returns by providing notice to HMRC in a reasonable form.

When handling amendments for Capital Gains Tax (CGT) on UK Property accounts, taxpayers face specific restrictions. Schedule 2 to the Finance Act 2019 dictates that amendments to a 60-day property return are only permitted to the extent they could have been included when the return was originally delivered.

Amendments cannot be made to the property return at any time on or after the date on which the person has submitted their Self Assessment return taking account of the disposal.

Once the taxpayer submits the Self Assessment return, it must include the final figures for the year, capturing any late-arising losses or adjustments that would otherwise necessitate an amendment to the standalone property return.

Time Limits for Statutory Amendments

Strict statutory time limits govern the window for amending a submitted tax return. Under section 9ZA(2) of TMA 1970, an individual may not make an amendment more than twelve months after the statutory filing date.  For claims made outside of a return, taxpayers generally have up to 12 months from the date HMRC receives the original claim to amend it.

Table: Key Amendment Time Limits

MTD ITSA Implications for the 2026/27 Tax Year

The introduction of Making Tax Digital for Income Tax (MTD ITSA) in the 2026/27 tax year significantly alters reporting mechanics but leaves the final amendment window intact. Taxpayers mandated to use MTD ITSA must finalise and submit their end-of-year tax return by 31 January following the end of the tax year (e.g., 31 January 2028 for the 2026/27 tax year).

HMRC has confirmed a soft landing for penalties during the transitional 2026/27 year. Taxpayers will not incur penalty points for missing quarterly updates.  However, late payment penalties will apply to amounts due following an amendment or assessment.  During this first year, taxpayers benefit from a 30-day grace period from the payment due date before HMRC applies late payment penalties; for payments exceeding 31 days late, the penalty scales up to 3% of the tax owed at day 15, an additional 3% at day 30, plus an annualised 10% rate thereafter.

Interplay with HMRC Enquiries

Amending a submitted tax return while an HMRC enquiry is active triggers specific procedural rules. If a company amends its return during an enquiry into that return, the amendment does not restrict the scope of the officer’s enquiry.  HMRC will take the amendment into account alongside any matters arising during the investigation.

Crucially, the tax effect of the amendment is deferred. Any resulting changes to the tax charge, or group relief consequences, only become legally effective once HMRC issues a closure notice to conclude the enquiry.

Remedies After the Statutory Deadline

When a taxpayer misses the 12-month deadline for amending a submitted tax return, the statutory right to amend falls away. If the taxpayer has overpaid tax, they must rely on a claim for Overpayment Relief.  The standard time limit for an overpayment relief claim is four years from the end of the relevant tax year for individuals, or four years from the end of the accounting period for companies.

Conversely, if an out-of-time error reveals underpaid tax, taxpayers should notify HMRC immediately. HMRC will typically recover the underpayment by issuing a discovery assessment under sections 34 or 36 of TMA 1970.  The assessment windows depend heavily on the taxpayer’s behaviour:

• Normal time limit: 4 years after the end of the relevant tax year for innocent errors.
• Careless conduct: 6 years after the end of the relevant tax year.
• Deliberate conduct or failure to notify: 20 years after the end of the relevant tax year.

Consider reviewing the specific penalty mitigation strategies available under the MTD ITSA regime for 2026/27, particularly regarding reasonable excuse defences for late payments resulting from retrospective amendments.