IHT400 is HMRC's full Inheritance Tax account. You must complete it as part of the probate or confirmation process if there's Inheritance Tax to pay, or if the estate doesn't qualify as an excepted estate. If tax is owed, the IHT400 has to reach HMRC within 12 months of the death and before you apply for probate, but the tax itself is due sooner.
Everything below comes from HMRC's IHT400 publication page and its rates and tables sheet, and the GOV.UK guides on valuing an estate and how Inheritance Tax works, as of October 2026.
When an estate needs the IHT400
Most estates don't. GOV.UK says most are excepted estates, which report a simpler estimate when applying for probate. You need the full IHT400 when there's Inheritance Tax to pay, or when the person who died, even with no tax due:
- Gave away over £250,000 in the 7 years before they died.
- Left an estate worth more than £3 million.
- Had foreign assets worth more than £100,000.
- Held assets worth over £250,000 in trust.
- Had trust assets pass to a surviving spouse, civil partner or charity, where the trust was worth £1 million or more, or £250,000 or more after deducting what passed to them.
The thresholds behind the decision
| Rule | Figure (GOV.UK, as of October 2026) |
|---|---|
| Inheritance Tax threshold (nil rate band) | £325,000 |
| Threshold when a home goes to children or grandchildren | Up to £500,000, for estates worth less than £2 million |
| Standard rate above the threshold | 40% |
| Reduced rate if 10% or more of the net estate goes to charity | 36% |
| Rate on lifetime transfers | 20% |
GOV.UK's own example: an estate worth £500,000 with a £325,000 threshold pays 40% of £175,000. Any unused threshold of a spouse or civil partner who died first can be added to the survivor's.
The deadline people get wrong
The 12-month limit is for the paperwork. The tax is due by the end of the sixth month after the death, and interest is charged from the day after. HMRC's table puts it plainly:
| Month the person died | Tax due | Interest charged from |
|---|---|---|
| January | 31 July | 1 August |
| April | 31 October | 1 November |
| July | 31 January | 1 February |
| October | 30 April | 1 May |
| December | 30 June | 1 July |
So most executors start paying Inheritance Tax before probate is granted, and before the IHT400 is even finished. You need an Inheritance Tax reference number from HMRC at least 3 weeks before paying.
How the form works
- Value everything the person owned on the date of death, their share of anything owned jointly, and gifts made in the 7 years before death.
- Download the interactive IHT400 and open it in Adobe Reader. You can't save a partly completed form, so gather the figures first.
- Complete the main form and the schedules that apply, IHT401 to IHT436, such as gifts, pensions, household goods and listed shares.
- Use the IHT400 calculation to work out the tax, and pay it.
- If you're applying in Northern Ireland, send form IHT421 with the IHT400. In England and Wales, HMRC sends you probate figures and a unique reference instead.
- Send everything to the address on the form.
Valuing jointly owned property
GOV.UK's worked example shows the detail that changes the figure. A home worth £200,000 owned with 3 other people gives a £50,000 share, and 10% (£5,000) comes off that share for joint ownership, leaving £45,000. In Scotland, £4,000 comes off the whole property before dividing it, so the same share is £49,000. Gifts count too: GOV.UK lists small gifts of £250 or less and the £3,000 annual exemption among the reliefs to check.
Gifts and the family home
Gifts are where many IHT400s grow. GOV.UK says people you give gifts to might have to pay Inheritance Tax, but only if you give away more than £325,000 and die within 7 years. A home given away counts as a gift if the giver dies within 7 years. If the giver keeps living there without paying rent at the going rate and their share of the bills, it's a gift with reservation, which is added back to the estate, and the 7-year rule doesn't apply to it.
The person dealing with the estate, the executor if there's a will, pays the tax from estate funds. GOV.UK says beneficiaries don't normally pay tax on what they inherit, though they may have related taxes, such as on rental income from a house they're left.
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After you send it
- HMRC sends a unique code confirming you've paid enough tax, usually within 20 working days of getting the IHT400 or the payment, whichever is later.
- For Northern Ireland applications, HMRC returns its part of the IHT421 within a similar 20 working days.
- If you haven't heard from HMRC 14 weeks after sending the IHT400, no further checks will be carried out.
For help, the rates sheet gives HMRC's Inheritance Tax helpline as 0300 123 1072, or +44 300 123 1072 from outside the UK.
The verdict
If the estate is small and simple, check the excepted estate rules first, because you may not need the IHT400 at all. If tax is due, work backwards from the six-month date, not the 12-month one: get the reference number early, value the estate, and pay before interest starts. Any Income Tax the person owed up to the date of death is a separate job, handled through returns such as the SA100, and an agent can deal with HMRC for you using form 64-8.
Frequently asked questions
When do I need to complete an IHT400?
When there's Inheritance Tax to pay, or the estate doesn't qualify as an excepted estate, for example because over £250,000 was given away in the 7 years before death or the estate is worth more than £3 million.
What is the deadline for the IHT400?
If the estate owes Inheritance Tax, you must report its value within one year using form IHT400, and before you apply for probate.
When is Inheritance Tax due?
By the end of the sixth month after the person dies. Interest is charged from the day after.
How long does HMRC take after an IHT400?
HMRC usually sends a code confirming you've paid enough tax within 20 working days of getting the IHT400 or the payment, whichever is later.
What is the Inheritance Tax threshold?
GOV.UK gives the threshold as £325,000, rising to £500,000 if a home is left to children or grandchildren and the estate is worth less than £2 million.
