A Comprehensive Guide on When and How to Complete the IHT400 Form
The IHT400 form is used to give HMRC full details of a person’s estate after they die. This includes their assets, debts, certain lifetime gifts, and any Inheritance Tax reliefs or exemptions being claimed.
You will usually need to complete an IHT400 if the estate does not qualify as an excepted estate or if Inheritance Tax is due. If you are unsure, see our guide to [What Is an Excepted Estate?].
Important
Always check GOV.UK for the most current version of the form before starting.
When Do You Need to Complete the IHT400?
Not every estate requires the IHT400. Whether you need to complete it depends on whether the estate qualifies as an excepted estate.
If it does, there is no need to submit the full IHT400. If it does not qualify, you must complete and submit the IHT400 to HMRC.
When you must use the IHT400
You must complete the IHT400 if the estate does not meet the criteria for any of the excepted estate.
This means the IHT400 is required where:
Important
Even where no Inheritance Tax is ultimately payable, you may still need to complete the IHT400 if the estate does not meet the excepted estate criteria. The IHT400 is about reporting, not just about paying tax
Deadlines You Must Know
There are two separate deadlines to be aware of when dealing with Inheritance Tax.
They are not the same, and the tax payment deadline arrives considerably earlier than the deadline for submitting the IHT400 form itself.
Paying the Inheritance Tax
Inheritance Tax is due by the end of the sixth month after the month in which the person died.
For example, if a person died on 15 March, the tax payment deadline would be 30 September of the same year. If the tax is not paid by this date, HMRC will begin charging interest on the outstanding amount.
Important
From 6 April 2025, HMRC charges late payment interest at the Bank of England base rate plus 4%. This rate changes whenever the Bank of England adjusts the base rate, so always check the current position on GOV.UK.
Submitting the IHT400 form
The IHT400 must be submitted to HMRC within 12 months of the date of death.
This is a separate deadline from the payment deadline.
Notice that the tax is due before the form deadline. This creates pressure to gather all valuations, calculate the liability and arrange payment within the first six months, while the form itself can technically be submitted up to a year after the death.
Important
You cannot wait until the 12-month deadline to start your IHT400 if tax is payable. The tax must be paid within six months, and HMRC will not issue the unique probate code until both the IHT400 and the tax payment have been received and processed.
Penalties for Late Filing and Payment
If the IHT400 is not submitted within the 12-month deadline, HMRC can impose penalties. The penalty structure is as follows:
Period of Delay
Penalty
Late submission (up to 6 months late) | £100 initial penalty |
More than 6 months late | Further £100 penalty |
More than 12 months late | Additional penalty of up to £3,000 |
Inaccurate return (gifts not reported etc.) | Up to 100% of the tax due |
In addition to these fixed penalties, interest continues to accrue on any unpaid tax from the due date. HMRC may waive penalties where the personal representative has a "reasonable excuse" for the delay.
Please refer to IHTM36023 - Late accounts: penalties chargeable - HMRC internal manual - GOV.UK for the penalties.
What You Need Before You Start
The IHT400 is an interactive PDF. It cannot save partially completed data, so you should gather all the necessary information before you begin.
Essential documents and information
Important
You must apply for an Inheritance Tax reference number before submitting the IHT400. Without this reference, HMRC will reject the form. Allow at least three weeks for the reference to arrive.
The Supplementary Schedules
The IHT400 is accompanied by supplementary schedules numbered IHT401 through IHT436. You only complete and submit the schedules that are relevant to the estate in question. The questions on pages 1, 5 and 6 of the main IHT400 form will direct you to the appropriate schedules.
Below is a summary of the most commonly used schedules.
Schedule
Description
IHT401/401a | Domicile outside the UK (IHT401 for deaths before 6 April 2025) or long-term UK residence (IHT401a for deaths on or after 6 April 2025) |
IHT402 | Claim to transfer unused nil rate band from a predeceased spouse or civil partner |
IHT403 | Gifts and other transfers of value made by the deceased in the seven years before death |
IHT404 | Jointly owned assets |
IHT405 | Houses, land, buildings and interests in land |
IHT406 | Bank and building society accounts |
IHT407 | Household and personal goods |
IHT409 | Pensions |
IHT410 | Life assurance and annuities |
IHT411 | Listed stocks and shares |
IHT412 | Unlisted stocks, shares and control holdings |
IHT413 | Business and partnership interests and assets (for claiming Business Property Relief) |
IHT414 | Agricultural Relief |
IHT417 | Foreign assets |
IHT418 | Assets held in trust |
IHT430 | Reduced rate of Inheritance Tax calculation (36% rate where 10% or more of the net estate is left to charity) |
IHT436 | Claim for transferable Residence Nil Rate Band |
Do not submit schedules that are not relevant to the estate. Sending unnecessary schedules slows down HMRC processing and can create confusion.
Step by Step Process for Completing the IHT400
Let’s have a walkthrough of the process from start to finish.
Step 1 - Determine whether the estate is excepted
Before doing anything else, assess whether the estate qualifies as an excepted estate.
Step 2 - Apply for an Inheritance Tax reference number
If the IHT400 is required, you must apply to HMRC for an Inheritance Tax reference number. This can be done online via GOV.UK or by posting form IHT422.
You should apply at least three weeks before you intend to submit the IHT400. The reference number is essential for all payment transactions and must be quoted on the form.
Step 3 - Gather all asset valuations and supporting documents
Collect comprehensive details of every asset the deceased owned at the date of death.
All assets must be valued at their open market value on the date of death. Property should be professionally valued, and listed shares should be valued using the closing price on the date of death.
You should also gather full details of any gifts made in the seven years before death and information about any trusts.
Step 4 - Complete the IHT400 and relevant supplementary schedules
Work through the main IHT400 form section by section. The questions on pages 1, 5 and 6 will direct you to the supplementary schedules you need to complete. Assets are reported across two columns on pages 7 and 8 of the form. Column A covers assets where the tax must be paid in full immediately (such as cash and most investments). Column B covers assets where the tax can be paid in annual instalments (such as property and business assets).
Step 5 - Calculate the tax
If you are completing the form without professional help, you can ask HMRC to calculate the tax for you by ticking the relevant box on the form.
Otherwise, use the IHT400 Calculation sheet or Schedule IHT430 (for the reduced rate) to work out the liability. The standard rate of Inheritance Tax is 40% on the value of the estate above the available nil rate band.
Step 6 - Arrange payment
Tax must be paid by the end of the sixth month after the month of death.
The most common method of payment is the Direct Payment Scheme, which allows funds to be released directly from the deceased's bank accounts to HMRC using form IHT423.
A separate IHT423 is needed for each bank or building society account. Other payment options include personal funds, loans, or paying by instalments for qualifying assets (using form IHT420).
Step 7 - Submit the IHT400 to HMRC
Send the completed and signed IHT400, all relevant supplementary schedules, any IHT423 forms for the Direct Payment Scheme and supporting documents to HMRC.
Step 8 - Receive the unique probate code
Once HMRC has processed the IHT400 and received any tax payment due, they will issue an acknowledgement letter containing a unique code.
This code is needed to complete your probate application in England and Wales. You can request that HMRC sends this code by email to speed up the process.
HMRC aims to process straightforward cases within 15 working days, although complex estates may take longer. It is generally advisable to wait at least 20 working days after submitting the IHT400 before applying for probate.
Step 9 - Apply for probate
Once you have received the unique code from HMRC, you can proceed with your probate application through HM Courts and Tribunals Service (HMCTS).
The code confirms that the Inheritance Tax position has been reported and any tax due has been paid or arrangements have been made.
Exemptions and Reliefs
Various exemptions and reliefs can reduce or eliminate the Inheritance Tax liability. The most common are summarised below.
Spouse or civil partner exemption
Assets passing to a surviving spouse or civil partner are fully exempt from Inheritance Tax, provided both the deceased and the surviving spouse are UK domiciled (or, for deaths on or after 6 April 2025, long term UK residents). There is no upper limit on this exemption.
Charity exemption
Assets left to a qualifying charity are exempt from Inheritance Tax. If the deceased left 10% or more of their net estate to charity, the estate may qualify for a reduced rate of Inheritance Tax at 36% instead of the standard 40%. This is claimed using Schedule IHT430.
Business Property Relief (BPR)
BPR can reduce the value of qualifying business assets by 100% or 50% depending on the type of asset. This relief is claimed using Schedule IHT413. From April 2026, the Government has announced that the 100% rate of BPR will be restricted to the first £1,000,000 of combined qualifying business and agricultural property, with a 50% rate applying thereafter.
Agricultural Property Relief (APR)
APR applies to the agricultural value of qualifying agricultural property and can provide relief at 100% or 50%. This is claimed using Schedule IHT414. The same restriction to £1,000,000 announced for BPR will also apply to APR from April 2026.
Transferable Nil Rate Band
Where the first spouse to die did not use their full nil rate band, the unused portion can be transferred to the surviving spouse's estate, potentially doubling the available threshold to £650,000. This is claimed using Schedule IHT402.
Residence Nil Rate Band (RNRB)
An additional £175,000 threshold is available where the deceased's main residence is left to direct descendants. Where both spouses qualify, the combined RNRB can reach £350,000 using Schedule IHT436. The RNRB is tapered for estates with a net value above £2,000,000.
Common Mistakes to Avoid
HMRC regularly identifies errors in IHT400 submissions that cause delays and can trigger penalties.
The most common mistakes include the following.
Important
HMRC can inspect records up to 20 years after Inheritance Tax is paid. Keep all supporting documents, valuations and calculations safe for the long term.
Changes from April 2025 and Forthcoming Changes
Several recent and forthcoming changes affect the IHT400 process and Inheritance Tax more broadly.
Long term UK residence rules (from 6 April 2025)
The previous deemed domicile rules for Inheritance Tax purposes have been replaced by a new long term UK residence test. This change affects how non UK nationals are treated for IHT purposes and is reflected in the updated IHT400 form (December 2025 version) and the new Schedule IHT401a.
Pensions and IHT (from 6 April 2027)
The Government has announced that unused pension funds and death benefits will be brought into a person's estate for Inheritance Tax purposes from 6 April 2027. This will apply to both defined contribution and defined benefit schemes, as well as to UK registered and qualifying non-UK pension schemes.
Restriction on BPR and APR (from April 2026)
The 100% rate of Business Property Relief and Agricultural Property Relief will be restricted to the first £1,000,000 of combined qualifying property. A 50% rate will apply to values above this threshold. This represents a significant change for agricultural and business estates and will affect the completion of Schedules IHT413 and IHT414.
Conclusion
Inheritance Tax administration is often more technical than it first appears. Even where the core facts seem straightforward, issues such as valuations, lifetime gifts, domicile, trusts and the correct application of reliefs and nil rate bands can materially affect the tax payable and the time it takes to finalise the estate. Where there is any uncertainty, taking advice early can help avoid delays, reduce the risk of errors, and provide reassurance that the position reported to HMRC is robust and properly supported.
How UKPA Can Help
UKPA can support personal representatives and families by providing clear, practical guidance through the Inheritance Tax process. We help you identify the reliefs and exemptions that may be available, confirm the correct treatment of lifetime gifts and any reservation of benefit concerns, and ensure valuations and supporting evidence are appropriate for HMRC purposes.
Simplify your task - Let us Handle your Property & Tax Filing.
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