IHT402 is the HMRC form executors use to move the unused Inheritance Tax nil rate band of a spouse or civil partner who died first onto the estate of the one who has just died. It goes in with the IHT400 and can lift the tax-free threshold from £325,000 to as much as £650,000. HMRC must receive it no later than 24 months after the end of the month in which the second person died.
Everything below comes from HMRC's IHT402 form (04/25), the GOV.UK guide to transferring the unused basic threshold and HMRC's IHT400 rates and tables, as of October 2026.
When the form applies
The IHT402 itself sets out four conditions. You fill it in if:
- the person who has just died, died on or after 9 October 2007
- their spouse or civil partner died before them
- the first estate didn't use up all of the nil rate band available to it
- you want to transfer the unused amount to the second estate
GOV.UK adds that the couple must have been married or in a civil partnership when the first death happened. The first death can be decades earlier: the form's own example uses a spouse who died in May 2006.
It's a percentage, not a pound figure
This is the part people miss. You don't transfer the leftover pounds from the first death. You work out what percentage of the band went unused back then, and that percentage is added to the band in force at the second death. A first death from years ago, when the band was lower, still carries its unused share forward at today's value.
| GOV.UK example | Band at first death | Used at first death | Unused | Band at second death | Threshold for second estate |
|---|---|---|---|---|---|
| Carole, then Simon | £325,000 | £130,000 to the children (40%) | 60% | £325,000 | £520,000 |
| David, then Mark | £250,000 | £50,000 to a friend (20%) | 80% | £325,000 | £585,000 |
Gifts to the surviving spouse or civil partner don't use up any band, which is why a first estate that left everything to the partner usually transfers the full 100%. The form caps the percentage there, so the most a second estate can get from this claim is double the current band.
How the boxes build the figure
- Box 9: the nil rate band in force when the first spouse died. HMRC's IHT400 rates and tables list every band back to 18 March 1986, when it was £71,000; it's been £325,000 since 6 April 2009.
- Box 10: the chargeable value of gifts the first spouse made in the 7 years before they died.
- Box 11: the band left for the first estate (box 9 minus box 10).
- Boxes 13 to 17: what the first estate passed to people other than the surviving partner, including joint assets, trust assets and gifts with reservation, after exemptions and reliefs. This total may be nil.
- Box 18: the band available to transfer.
- Box 19: box 18 divided by box 9, times 100. Use 4 decimal places and don't round up.
- Box 21: that percentage applied to the band at the second death, rounded up to the nearest pound.
Box 12 only matters for first deaths on or after 6 April 2017 where some residence nil rate band was used, and box 23 asks whether anyone was entitled to claim the legitim fund, because a claim can change the percentage.
When the first death was a long time ago
Box 9 always uses the band in force on the date the first spouse died, not today's. HMRC's rates and tables show, for example, £285,000 for 6 April 2006 to 5 April 2007, £300,000 for 2007 to 2008 and £312,000 for 2008 to 2009. The form's own deadline example uses that kind of gap: a spouse who died on 15 May 2006 and a second death on 10 October 2007, with the IHT402 due by 31 October 2009.
Papers to send with it
- A copy of the grant of representation for the first estate (confirmation in Scotland). If nobody took out a grant, send a copy of the death certificate instead.
- A copy of the first spouse's will and any codicils, if there was a will.
- A copy of any deed of variation or similar document that changed who inherited.
The form tells you to track down whoever acted for the first estate, such as the executor, the solicitor or family members, and to make full enquiries so the figures are right. For an old death, that hunt for paperwork takes longest, so start it when you start the IHT400.
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IHT402, IHT217 or IHT436
| Form | Use it for |
|---|---|
| IHT402 | Transferring the unused basic nil rate band, sent with the IHT400 |
| IHT217 | The same transfer for an excepted estate that doesn't need a full IHT400 |
| IHT436 | Transferring an unused residence nil rate band, alongside the IHT435 claim |
The residence band transfer works even if the first partner died before 6 April 2017, when that band didn't exist yet. The survivor has to leave a home to direct descendants and include it in their estate; it doesn't have to be the home the couple shared. Don't confuse any of this with the Marriage Allowance, which shares unused income tax allowance between living partners. The nil rate band transfer is a separate claim made after the second death.
My verdict
If a widow, widower or surviving civil partner has died and the first estate mostly went to them, an IHT402 is often the single biggest saving in the whole Inheritance Tax account. Find the first death's grant and will early, work the percentage to 4 decimal places, and get the form in with the IHT400 well inside the 24-month limit. Keep the UK tax year dates to hand too, because the band you use depends on the date of each death.
Frequently asked questions
What is form IHT402 used for?
It's used with the IHT400 to transfer any unused Inheritance Tax nil rate band from a spouse or civil partner who died first to the estate of the one who has just died.
What's the deadline for an IHT402?
HMRC must receive it no later than 24 months after the end of the month in which the second person died.
How much can be transferred with IHT402?
The unused percentage of the first band, up to 100%, applied to the band at the second death. With the band at £325,000 that can give a threshold of up to £650,000.
What documents go with the IHT402?
Copies of the grant of representation for the first estate (or the death certificate if there was no grant), the will, and any deed of variation.
Is IHT402 the same as IHT436?
No. IHT402 transfers the basic nil rate band. IHT436 transfers an unused residence nil rate band.
