How to Complete the IHT400 Inheritance Tax Account (2026 Guide)

The IHT400 is the full Inheritance Tax account that the personal representatives (executors or administrators) of an estate must submit to HMRC when Inheritance Tax is due or HMRC needs full details of the estate. It is a substantial form with many supplementary schedules, and it sits at the heart of the probate process. This guide explains when you need it, what to fill in, and how the deadlines and payment work.

To estimate the tax bill before you start, use the Inheritance Tax Calculator. For a screen-by-screen guide to the form itself, see the IHT400 Walkthrough.

1. Do you actually need an IHT400?

Most estates are excepted estates and do not need a full IHT400. You generally avoid the IHT400 if there is no Inheritance Tax to pay and the estate is below the relevant thresholds. The old paper IHT205 form was withdrawn for deaths on or after 1 January 2022 — for excepted estates you now simply report values directly when applying for probate, with no full account.

You must complete the IHT400 if any of these apply:

• There is Inheritance Tax to pay.
• The estate is worth more than £3 million (gross).
• The deceased gave away more than £250,000 in the seven years before death.
• The deceased held more than £250,000 in trust, or had foreign assets worth more than £100,000.
• The estate is otherwise outside the excepted-estate conditions.

2. The thresholds and rate that drive the bill

Inheritance Tax is charged at 40% on the value of an estate above the available threshold. The headline figures (frozen for 2026-27) are:

A married couple or civil partners can transfer any unused NRB and RNRB to the survivor, so a surviving spouse’s estate can have up to £1 million of allowances before any tax is due.

3. The IHT400 and its schedules

The IHT400 itself is the summary; the detail goes on supplementary schedules, of which you complete only the ones relevant to the estate. Common ones include:

• IHT405 — houses, land and buildings.
• IHT406 — bank and building society accounts and National Savings.
• IHT407 — household and personal goods.
• IHT403 — gifts and other transfers made in the 7 years before death.
• IHT402 — claiming a deceased spouse’s unused nil-rate band.
• IHT435 / IHT436 — claiming and transferring the residence nil-rate band.

The IHT400 Calculation pages then bring the totals together to work out the tax.

4. Deadlines that matter

There are two distinct deadlines and they catch executors out:

• Submit the IHT400 within 12 months of the end of the month in which the person died.
• Pay the Inheritance Tax within 6 months of the end of the month of death — interest runs from that point even though the form deadline is longer.

In practice you usually pay (at least an initial amount) when you send the IHT400, because you need HMRC’s acknowledgement code before you can apply for probate.

5. Paying IHT before probate — the chicken-and-egg problem

Executors face a classic problem: you often need to pay the tax to get probate, but you cannot access the deceased’s money without probate. The solutions:

• Direct Payment Scheme (form IHT423): participating banks, building societies and NS&I release funds from the deceased’s accounts directly to HMRC.
• Tax in instalments: tax on land, certain shares and some business assets can be paid in 10 equal annual instalments (interest applies).
• Grant on credit: in hardship cases, HMRC may grant probate before full payment.

Once HMRC has the IHT400 and payment, it issues a unique reference code (and, for Northern Ireland probate, completes and returns IHT421) that you submit with your probate application.

Estimate first, then file

Before tackling the form, get a clear view of the likely bill. Use the Inheritance Tax Calculator to model the nil-rate bands, residence nil-rate band, and 40% charge, then follow the IHT400 Walkthrough to complete the account itself.