Form IHT400 is the full inheritance tax account that personal representatives send to HMRC when someone dies and the estate either owes inheritance tax or does not qualify as an "excepted estate". It must be sent within 12 months of the death, and you cannot apply for probate until it has been processed and HMRC has sent a unique code. Any tax is due earlier, by the end of the sixth month after death, with late payment interest currently charged at 7.75%.
Do you need an IHT400?
For deaths on or after 1 January 2022, many estates do not need an IHT400 at all. Their details are reported on the probate application instead. HMRC recognises three types of excepted estate:
- Low value estates. The gross value does not exceed the nil-rate band of £325,000, or twice that where unused nil-rate band is transferred from a spouse or civil partner who died first. Further conditions apply: trust assets no more than £250,000 and in a single trust, foreign assets no more than £100,000, specified lifetime gifts no more than £250,000, and no gift with reservation of benefit;
- Exempt estates. Gross value up to £3 million, with no tax because of the spouse or civil partner exemption or the charity exemption alone. No other relief can be counted;
- Non-long-term UK residents. For deaths on or after 6 April 2025, people who were never long-term UK resident (for earlier deaths, foreign domiciliaries), whose UK estate is no more than £150,000 and consists only of cash or listed shares and securities. These estates use form IHT207 rather than the probate application.
If the estate fails any condition, for example because business property relief is needed to bring the tax to nil, or because the gross value is above the threshold even though the net value is not, an IHT400 is required.
The form and its schedules
The IHT400 itself collects the deceased's details, the overall estate figures and the tax calculation. The detail goes on schedules, which you complete only where relevant. The questions on pages 5 and 6 of the form tell you which apply. The main ones are:
| Schedule | Covers |
|---|---|
| IHT402 | Claim to transfer unused nil-rate band |
| IHT403 | Gifts and other transfers of value |
| IHT404 | Jointly owned assets |
| IHT405 | Houses, land, buildings and interests in land |
| IHT406 | Bank and building society accounts and National Savings and Investments |
| IHT409 | Pensions |
| IHT411 / IHT412 | Listed shares; unlisted shares and control holdings |
| IHT413 / IHT414 | Business and partnership interests (business relief); agricultural relief |
| IHT417 / IHT418 | Foreign assets; assets held in trust |
| IHT419 | Debts owed by the deceased |
| IHT430 | Reduced rate of inheritance tax (charity) |
| IHT435 / IHT436 | Residence nil-rate band; transfer of unused residence nil-rate band |
Two schedules are administrative rather than about assets. IHT422 applies for an inheritance tax reference, which you need before paying. IHT423 asks a bank or investment manager to pay tax direct to HMRC from the deceased's accounts, so the executors do not have to find the money before the grant. In Northern Ireland, IHT421 (probate summary) goes to the court; in England and Wales the grant application uses the unique code HMRC sends once the IHT400 has been processed.
Working out the tax on the form
The calculation runs from gross assets, less debts and funeral costs, less exemptions and reliefs, to the chargeable estate. Against that the estate sets the nil-rate band of £325,000, any transferred nil-rate band, and the residence nil-rate band of up to £175,000 where a home passes to direct descendants. The residence band is tapered by £1 for every £2 the estate exceeds £2 million. Gifts made in the seven years before death are reported on IHT403 and are taken into account in the calculation. Tax is charged at 40% on the balance, or 36% where at least 10% of the net estate goes to charity.
Each claim has its own evidence. Transferring a spouse's unused nil-rate band on IHT402 needs details of the first death, and the claim deadline is 24 months from the end of the month of death. Business and agricultural relief claims need accounts, share registers and a reasoned case that the conditions are met. Our guide to inheritance tax rules explains the reliefs themselves.
Deadlines, payment and penalties
- Payment. Tax is due by the end of the sixth month after the month of death. HMRC charges interest after that, at 7.75% since 9 January 2026. Tax on land, buildings and certain shares and business assets can be paid in ten annual instalments;
- The account. Due within 12 months from the end of the month of death;
- Late account penalties. Under section 245 of the Inheritance Tax Act 1984, a penalty of £100, a further £100 if the account is still outstanding six months later, and up to £3,000 if it is more than a year late and tax would have been shown as due.
Because the tax deadline falls six months before the account deadline, executors should start valuations straight away. If values or liabilities change after the IHT400 has been sent, for example where a provisional estimate is replaced by a final figure, HMRC must be told so the tax can be recalculated.
Common mistakes
- Estimated values. Using a rough figure for property or unquoted shares instead of a proper valuation at the date of death;
- Missing gifts. Lifetime gifts in the previous seven years, including regular transfers, change both the nil-rate band and the tax;
- Joint assets. Treating jointly held assets as outside the estate when the deceased's share must be included;
- Pensions. Answering the pension questions without checking the scheme details, when IHT409 may need to be completed;
- Variations. Not reflecting a deed of variation that changes who inherits and therefore the exemptions.
The IHT400 is the executor's legal responsibility, as set out in our guide to being an executor. Acumon's probate accountants prepare the IHT400 and schedules, obtain valuations, and deal with HMRC's questions after submission, and our inheritance tax planning team can review the reliefs available before the account is filed.