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Receiving a compliance check letter from HMRC after submitting an IHT400 can feel unsettling. HMRC's own IHT400 notes describe the review as a normal part of the process: once it has returned your probate values and code, “we'll look at form IHT400 in more detail. We may ask you questions to help us understand what you've said on the form and any schedules.” This guide explains what a compliance check is, how it differs from a formal enquiry, what HMRC asks for, and how to respond. For guidance on the probate process itself, see our complete UK probate guide.
An IHT compliance check is HMRC's formal process for verifying that an Inheritance Tax return — whether a full IHT400 or the figures reported for an excepted estate — is accurate and complete. HMRC has the legal power under the Inheritance Tax Act 1984 and the Finance Act 2008 to open enquiries into IHT returns, request supporting documents, and — where it finds errors — issue amended assessments and charge penalties.
A compliance check begins with a letter from HMRC. It will typically reference a specific aspect of the return — a property valuation, a gift, an allowance claim — and ask you to provide supporting evidence. HMRC's inheritance tax post goes to Inheritance Tax, HM Revenue and Customs, BX9 1HT, but reply to whatever address the letter itself gives.
The tone of the letter is usually formal but not accusatory. HMRC will refer to its powers under specific legislation and set a deadline for your response. Read it carefully — the specific documents or information requested will be listed, often in a numbered schedule.
These three terms describe different levels of HMRC scrutiny, and understanding the distinction matters:
For most executors a compliance check letter means the first of these — a request for supporting evidence. What the letter actually says, and which legislation it cites, is what tells you which one you have.
HMRC does not publish how it selects returns for a check, and no official source ranks the reasons. The areas its guidance and forms show it looking at are these:
HMRC's compliance check letter will usually request some or all of the following, depending on the trigger:
The letter sets its own response deadline; HMRC does not publish a standard period for inheritance tax compliance letters, so read the date on the letter rather than working to a rule of thumb. Where a formal information notice is issued under Schedule 36 to the Finance Act 2008, you can appeal it in writing within 30 days of receiving it. If you need longer to gather documents, write and say so before the deadline passes. If you do not respond at all, HMRC can:
If you need more time, telephone the HMRC Inheritance Tax team (0300 123 1072) or write to the address on the letter explaining the position. A short extension (2–4 weeks) is almost always granted for straightforward requests.
A well-organised response is the fastest route to closing the compliance check. Follow these principles:
For a detailed step-by-step on writing the response letter, see our guide on how to respond to an HMRC probate query.
Many compliance checks are a request for documents the executor already has. Some turn on questions where the rules are genuinely intricate:
A chartered tax adviser or probate solicitor can correspond with HMRC on your behalf and take a valuation dispute up with the Valuation Office Agency. No official source publishes what that costs, so ask for a quote before instructing anyone. Reasonable professional fees for administering the estate are generally payable from the estate.
If you want to understand whether doing probate yourself was the right call in your situation, see our guide on DIY probate vs using a solicitor.
HMRC's penalty regime for IHT errors is based on the behaviour that led to the error, not just its size:
Penalties are reduced for voluntary disclosure and co-operation. An executor who promptly corrects an error and co-operates fully will receive a substantially reduced penalty compared to one who delays or provides misleading information.
Where a compliance check reveals that additional IHT was due, HMRC charges interest from the date the tax was originally payable to the date of payment. HMRC's IHT400 notes give that start date precisely: “The law says that we must charge interest from the first day of the seventh month after the month in which the person died.” A death on 7 January means interest from 1 August.
Since 6 April 2025 the late payment rate has been the Bank of England base rate plus 4 percentage points. It has been 7.75% since 9 January 2026. It moves whenever the base rate moves, so check HMRC's rates page rather than relying on a figure quoted anywhere else, including here.
For broader context on how IHT timing and interest interact, see our guide to probate delays and IHT interest.
Once HMRC has reviewed your response, one of three outcomes follows:
Not necessarily. HMRC's own notes describe looking at the IHT400 in more detail after the grant stage as normal, and say it “may ask you questions to help us understand what you've said on the form and any schedules”. A check can end with the original return confirmed and no further tax due.
Usually. A compliance check that starts after the grant does not disturb it. But you cannot apply in the first place until HMRC has sent you its unique code confirming enough tax has been paid — since 18 January 2024 that code has replaced the IHT421 probate summary for applicants in England and Wales. IHT421 is still used in Northern Ireland, and form C1, ‘Inventory’, in Scotland. See our guide on probate delayed by HMRC.
If a compliance check reveals that additional IHT was due and the estate has already been distributed to beneficiaries, the executor is personally liable to pay the additional tax. This is one reason why executors should retain estate funds until HMRC has confirmed the IHT account is closed. See our guide on executor personal liability.
HMRC does not publish average timescales for inheritance tax compliance checks, so no honest figure can be given here. What is within your control is the response: HMRC's letter sets a deadline, and a valuation dispute runs until the Valuation Office Agency and you agree a figure — or, if you cannot, until the tribunal decides.
Yes. You have 30 days from HMRC's decision to appeal to the First-tier Tribunal (Tax Chamber). You can also request a statutory review by HMRC's review team before proceeding to tribunal. Most appeals settle by agreement before a tribunal hearing.
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