If you do not file a Self Assessment return by the filing date, HMRC can issue a determination: an estimate of your tax under section 28C of the Taxes Management Act 1970 that is treated as your self assessment and can be enforced. You cannot appeal against it. The only way to displace it is to file the actual return within the later of three years from the filing date and 12 months from the date of the determination.

What is an HMRC determination?

Section 28C TMA 1970 applies where HMRC have given you notice to file a return under section 8 (individuals) or 8A (trustees) and the return is not delivered by the filing date. An HMRC officer may then determine, to the best of their information and belief, the income tax and capital gains tax you are chargeable to for the year and the income tax payable. Notice must be served on you and must state the date it is issued (section 28C(2)).

Until it is superseded by a real self assessment, the determination has effect for the payment, collection and recovery, interest and miscellaneous parts of TMA 1970 as if it were your self assessment (section 28C(3)). HMRC’s Self Assessment Legal Framework manual (SALF209) explains the consequences:

  • the tax is payable and enforceable;
  • it is due on the date that would have applied had the return been filed on time;
  • it sets the level of payments on account for the following year.

HMRC’s Debt Management manual (DMBM518010) describes the purpose as raising a charge large enough to prompt the taxpayer to file and pay, or to contact HMRC. It also says that a claim to reduce payments on account cannot be made against a year for which a determination has been raised.

When can HMRC make a determination?

Only after the filing date has passed without a return, and only before the end of three years beginning with the filing date (section 28C(5)(a)). The filing date is 31 January after the end of the tax year or, if the notice to file was given after 31 October, three months from the date of the notice (section 28C(6)). DMBM518010 warns that a determination raised outside the three year limit is invalid.

In compliance cases HMRC’s Enquiry Manual (EM2027) says caseworkers ask Debt Management to issue the determination and must make sure the figure is to the best of their information and belief. It suggests the most effective time is within 12 months of the filing date, typically after the six month late filing penalty has been charged. As a matter of policy, DMBM518010 says HMRC give 30 days after a determination for the return to be filed before taking enforcement action, although they can still contact you in that period.

Why can’t you appeal against a determination?

Because the law does not give a right of appeal, and it does not need to. SALF209 and DMBM518010 both state that there is no right of appeal against a determination. The remedy is built into section 28C itself: once you file the return, your self assessment automatically replaces the determination, without the need for an appeal or any agreement with HMRC.

That distinguishes a determination from other HMRC charges. A discovery assessment made where no return was filed, and a PAYE determination of an employer’s liability, are both appealable decisions listed in HMRC’s appeals guidance (ARTG2160). It also means the reasonable excuse and late appeal routes do not apply to a determination; see late appeals for where they do.

How do you displace a determination?

File the return. Under section 28C(5), a self assessment superseding a determination must be made either before the end of three years beginning with the filing date or, if later, before the end of 12 months beginning with the date of the determination. When it is filed in time, DMBM518010 says the determined tax is automatically amended to the figure on the return, and related interest, late payment penalties and payments on account are amended with it.

Two further points follow from the legislation:

  • Any balance payable or repayable because the return supersedes the determination falls due on the normal balancing payment date in section 59B(3) or (4), not on a new date (section 59B(5A)). Interest therefore runs from the original due date on any tax that remains payable.
  • If HMRC have already started recovery proceedings, they can continue them for the tax shown in your self assessment (section 28C(4)), and the same applies to direct recovery from bank accounts (section 28C(4A)).

Illustration

Illustration only. A landlord received notice to file a 2022 to 2023 return but never filed. The filing date was 31 January 2024, so the three year window beginning on that date ends on 30 January 2027. HMRC issue a determination dated 1 September 2026 charging £8,000. The later of the two limits is the 12 months beginning 1 September 2026, which ends on 31 August 2027. If his actual return, showing £3,000 of tax, is filed by then, it replaces the determination and he owes £3,000 plus interest from 31 January 2024. If he misses that date, the £8,000 stands and his only remaining option is special relief.

Do determinations affect penalties?

Late filing penalties and determinations are separate. DMBM518010 states that they are raised independently, and filing a return to displace a determination does not cancel late filing penalties already charged. Our guide to Self Assessment deadlines and penalties sets out the penalty stages.

Do companies face determinations too?

Yes. For corporation tax, Schedule 18 to the Finance Act 1998 contains a parallel power. HMRC’s Company Taxation Manual explains that:

  • a determination can be made once the filing date has passed (CTM95310) but not later than three years after the date on which it could first be made (CTM95390);
  • it has the same effect as a company self assessment for payment, collection, interest and tax related penalties (paragraph 39, CTM95380);
  • a return supersedes it if delivered by the later of the time limit for making the determination and 12 months after the date of the determination (paragraph 40, CTM95400).

What if it is too late to file?

Once both time limits have passed, the determination stands as your liability. The legislation then offers one narrow route: special relief under paragraph 3A of Schedule 1AB TMA 1970 (and paragraph 51BA of Schedule 18 for companies). It requires HMRC to accept that recovering the amount would be unconscionable, that your other tax affairs are up to date, and normally that you have not relied on the relief before. HMRC’s Self Assessment Claims Manual (SACM12220) confirms special relief applies only to amounts charged in determinations where no other statutory remedy exists. It is designed for cases where ordinary overpayment relief is barred, for example because more than four years have passed since the end of the tax year.

What are the common mistakes?

  • Sending HMRC an appeal or a letter disputing the figure instead of filing the return. Neither displaces the determination.
  • Filing a return for the wrong year, or an incomplete one, and assuming the determination has gone.
  • Waiting until enforcement starts. HMRC can pursue the determined amount, including through the courts, while the return is outstanding.
  • Miscounting the deadline. It is the later of three years beginning with the filing date and 12 months beginning with the date on the determination, not the date you received it.
  • Expecting HMRC to withdraw a determination because it is too high. SACM12240 says the fact that a determination exceeds the real liability is not, on its own, enough for special relief.

If HMRC opens a check into your return, tax investigation insurance pays your accountant’s fees. Solar Protect cover pays up to £100,000 with no excess; it never pays tax, interest or penalties. Read how our cover works or get a quote.

Related Accountapedia entries

Sources

Reviewed by Christine Anderson, Broker, Solar Protect. Last reviewed 8 October 2026. Part of Accountapedia, the Solar Protect guide to UK tax and accounting. This page is general information, not personalised advice.