Inheritance Tax Late Penalties Surge 35% as Families Struggle With 122-Question Form

Inheritance tax late penalties rose 35% over the past five years, with HMRC issuing fines against 5,200 estates in 2024-25, up from 3,850 five years earlier, according to Freedom of Information data obtained by TWM Solicitors.

The total value of those penalties reached £3.1m in 2024-25 alone. That figure puts a sharper edge on what many bereaved families still treat as routine paperwork, when in practice the IHT400 return is one of the more technically demanding documents HMRC asks any individual to complete.

Understanding how inheritance tax late penalties accumulate starts with the primary source. The HMRC Internal Manual (IHTM36023) sets out that the fine for late filing of the IHT400 begins at £200 and rises by £400 for each subsequent month, up to a maximum of £3,000. Some published accounts of the FOI data cited an initial penalty of £100; the HMRC manual is the authoritative source and gives £200 as the opening charge.

The backdrop is well established. IHT is charged at 40% on the value of an estate above the £325,000 nil-rate band, according to the Office for Budget Responsibility. That threshold has been frozen since 2009, drawing in estates that would not have qualified a generation ago. An average house in many parts of England now exceeds it without any other assets in the picture.

How the IHT400 Catches Families Off Guard

The main IHT return contains 122 questions. Depending on the composition of the estate, it must often be supplemented by more than 30 additional schedules covering specific asset classes or circumstances. Residential property must be valued professionally; a market estimate or an estate agent’s figure does not meet HMRC’s requirements. Shares and certain other assets must be valued using specific technical methods for IHT purposes, and sourcing correct valuations takes time even for those who know what they are looking for.

Executors face a separate challenge in simply accounting for everything. Tracing all bank accounts, investments, and historical gifts, including those relevant under the seven-year rule, can require written requests to multiple institutions. Many banks still process such requests only by post, adding weeks to an already pressured timeline.

Duncan Mitchell-Innes, partner and deputy head of private client at TWM, said: ‘People often underestimate the complexity of the UK’s IHT rules. What seems like a straightforward task can quickly become time-consuming and technically challenging, particularly when HMRC requires extensive supporting evidence. This can lead to penalties if deadlines are missed.’

Mitchell-Innes added that families managing their own returns frequently miss reliefs they are entitled to. Gifts made out of surplus income, or those made more than seven years before death, may be exempt from IHT altogether, but identifying them and assembling the supporting evidence is a task many executors do not know they need to do. ‘Reliefs aren’t applied automatically. People must actively claim reliefs and exemptions and find the evidence to support them where needed, which can be time-consuming. Without proper advice, families risk penalties and leaving valuable reliefs unclaimed,’ he said.

Inheritance Tax Late Penalties: Deadlines and a Step That Can Help

Two deadlines govern the process. The IHT payment falls due six months from the end of the month of death, with interest accruing on any unpaid balance from that date. The IHT400 filing deadline is 12 months from the end of the month of death, per GoFile’s guide to key IHT dates. Executors who cannot complete valuations in time have one practical option: filing the IHT400 with estimated figures initially, which stops the late-filing penalty clock while the full picture is assembled.

The volume of inheritance tax late penalties is set to grow further after April 2027. Under the GOV.UK technical note on IHT on pensions, from 6 April 2027 most unused pension funds and pension death benefits will be brought within the taxable estate. The change will pull a materially larger cohort of families into the IHT400 process for the first time. Beneficiaries who receive pension property will also become jointly and severally liable, alongside personal representatives, for any IHT attributable to that property.

Personal representatives who have never filed an IHT return have roughly two years to understand what the process involves. The first affected estates will be those where death falls after 6 April 2027. Miss the 12-month filing window by a single month, and the penalty notice follows as a matter of course.