Tax · United Kingdom
Revenue determination (section 28C, Taxes Management Act 1970) — HMRC's estimate when no return was filed
A revenue determination is HMRC's own estimate of the tax you owe, made because a Self Assessment return was required and never filed. It cannot be appealed. The only mechanism that replaces the figure is filing the actual return, within a time limit.
How serious: enforcement closeAlso called: Determination notice, HMRC determination, Section 28C determination
When you were required to file a Self Assessment return and did not, an HMRC officer can determine the amounts 'to the best of his information and belief'. That estimate is the revenue determination, made under section 28C of the Taxes Management Act 1970.
It is deliberately not appealable. Until the real return is filed, the estimate is fully enforceable as if you had declared it yourself. It also sets your payments on account for the next year.
The figure can be replaced, but only one way: by filing the actual return within the statutory window. Once that window closes, the estimate becomes final — even if the real figure would have been lower.
Who sends it
HM Revenue and Customs (HMRC), the UK's tax authority.
An HMRC letter stating that because your tax return for a named year was not received, HMRC has determined the tax due. It shows an estimated amount, a demand for payment, and wording that the determination stands until you send in your return.
The deadline
No appeal exists — 'There's no right of appeal against this estimate.' It can only be displaced by filing the actual return: a superseding self-assessment must be made within the s28C(5) limits — 'before the end of the period of 3 years beginning with the filing date' or, if later, 'before the end of the period of twelve months beginning with the date of the determination'.
There is no appeal: 'There's no right of appeal against this estimate.' The determination can only be displaced by filing the actual return — a superseding self-assessment must be made within the s28C(5) limits: 'before the end of the period of 3 years beginning with the filing date' or, if later, 'before the end of the period of twelve months beginning with the date of the determination'. The 12-month window runs from the date of the determination.
If you do nothing
The estimated tax is legally collectable: the determination 'shall have effect... as if it were such a self-assessment' until superseded by your real return. You 'still have to pay the amount due', and 'HMRC may take legal action to recover the amount due and any costs'. Once the supersession window closes, the estimate becomes final — even if the real figure would have been lower.
Compute your date
The rule above is what the law sets. Put in the dates on your own letter and it becomes a date.
Don't miss this date
We'll email you 7, 3 and 1 day before, and on the day — at 9:00 your time.
We keep only what the reminder needs — type, dates, sender — encrypted. Delete it any time.
How it escalates
- 01The determined amount is enforced as an ordinary tax debt — HMRC's debt process applies: debt collection agencies, taking control of goods, direct recovery from bank accounts, court action.
- 02Late-filing penalties on the missing return continue to accrue separately.
- 03After the statutory window (12 months from the determination, if the 3-year limit has passed) the right to replace the estimate with your actual figures is lost permanently.
How to respond
Response types
- Confirm receiptSuperseding self-assessment - filing the outstanding Self Assessment return · Taxes Management Act 1970, ss9 and 28C(3), (5)Form: SA100 with the relevant supplementary pages (paper), or the online Self Assessment return
- Ask for instalmentsTime to Pay arrangementForm: HMRC online Self Assessment payment plan, or an arrangement agreed with the Payment Support Service on 0300 123 1813
Where and how
- File your Self Assessment tax return online
- Post (first class / ordinary mail)
- Royal Mail Signed For / Special Delivery Guaranteed
- Telephone
What makes it count
Nothing about a determination is preserved by posting: the return counts when HMRC receives it, or when the online service timestamps it, and the s28C(5) window is a hard statutory limit with no roll-forward and no extension. Filing online is therefore the safer route near the limit, and the twelve months run from the issue date the notice prints under s28C(2), not from the day the letter arrived.
Common questions
Can I appeal the amount?
No. There is no right of appeal against the estimate. Filing the actual return is the only mechanism that replaces it.
How long do I have to file the real return?
Within 3 years beginning with the filing date, or, if later, within 12 months beginning with the date of the determination (s28C(5)).
Do I have to pay an estimate?
Yes. The determination has effect as if it were your own self-assessment until a real return supersedes it, and HMRC may take legal action to recover it.
Sources
Facts verified against the sources below on 28 August 2026.