Penalty, assessment, or "we are checking": the letters with real clocks
Last reviewed 1 September 2026 · How Tax Letters checks its facts
Most of this site is about nudge letters, whose reply dates are set by HMRC's letter rather than by law. This page is the exception, and it exists so nobody learns the difference too late. If your letter is a penalty notice, a tax assessment or determination, or says a compliance check or enquiry has started, different rules apply.
Usually 30 days from the date of issue
Appeal rights against penalties and assessments usually run for 30 days from the date the notice was issued. That window is set by law. It is not extended just by asking, and waiting spends it.
Source: GOV.UK, appeal against a penalty (undated, checked 29 Aug 2026)
What each letter means
HMRC has charged a fixed or calculated amount. You can pay, or appeal within the window if you disagree or had a reasonable excuse. The notice itself states the date and the route.
HMRC has decided what it thinks you owe, sometimes by estimate. Left unchallenged inside the window, it generally stands. If the figure is wrong, the appeal window is where that gets said. A Simple Assessment has its own, gentler first step: query it within 60 days (Taxes Management Act 1970, section 31AA(3)).
HMRC is formally looking at a return or period. There may be no appeal deadline on the opening letter itself, but requests inside a check, especially formal information notices, carry their own time limits and penalties for silence. This is the point where professional help usually earns its fee.
Do these three things today
- Find the date of issue on the letter and count 30 days. That is your working window unless the letter states another.
- Decide nothing by default. Not appealing is a decision too, and it is the one silence makes for you.
- If you want to challenge it, start now: GOV.UK explains how to appeal, and an adviser can run it for you.
These letters are where advisers earn their keep
Some letters are worth handing to a specialist, and knowing when is half the value of a check. An adviser will treat what you say in confidence and will not judge how it got here. If we cannot point you anywhere useful, we will say so.
You can deal with HMRC directly, free, without any adviser. If money is tight: TaxAid (low incomes, older people included) and Citizens Advice help for free.
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