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IHT402 is the supplementary schedule used to claim the transferable nil rate band (TNRB) — the portion of a deceased spouse or civil partner's inheritance tax allowance that was unused on their death and can now be applied to the second estate. Submitting IHT402 correctly can reduce or eliminate inheritance tax on the second death, potentially saving tens of thousands of pounds.
Every individual has a nil rate band (NRB) — the amount they can leave free of inheritance tax. In 2026/27, the NRB is £325,000. When a married person or civil partner dies and leaves assets to their surviving spouse, those assets are usually exempt from inheritance tax entirely. As a result, the first spouse may use little or none of their NRB.
IHT402 allows that unused NRB to be transferred to the surviving partner's estate when they die. The key principle is that the transfer is calculated as a percentage of the NRB, not a fixed cash amount. That percentage is then applied to the NRB in force at the date of the second death.
This means that even if the first spouse died many years ago when the NRB was lower, the transferred allowance is uplifted to today's value — a significant benefit for older estates.
Example: Margaret died in 2005 when the NRB was £275,000. She left her entire estate to her husband David, so her NRB was 100% unused. David dies in 2026 when the NRB is £325,000. His estate can claim 100% of £325,000 (his own NRB) plus 100% of £325,000 (the transferred NRB) = £650,000 combined NRB.
You need to complete IHT402 when all of the following apply:
If the deceased was widowed more than once, you may be able to transfer unused NRB from multiple previous spouses, up to a maximum of 100% of the NRB at the second death (so the combined NRB can never exceed twice the current NRB, regardless of how many previous spouses there were).
The transfer is not automatic and it has a deadline. The form says so in terms: “Since the transfer does not happen automatically, you must fill in this form and make a claim to transfer it.” The claim must reach HMRC “no later than 24 months after the end of the month in which the deceased died” — the second death, not the first.
The calculation has two steps:
Patricia left her entire estate to her husband Robert. The NRB at her death was £325,000 and she used none of it (because the spouse exemption applied). Percentage unused: 100%. Robert dies when the NRB is still £325,000. Transferable NRB = 100% × £325,000 = £325,000. Robert's combined NRB = £650,000.
Jean died when the NRB was £325,000. She left £100,000 to her children (using £100,000 of her NRB) and the rest to her husband. Unused NRB = £225,000. The form asks for that as a percentage at box 19 — £225,000 ÷ £325,000 × 100 = 69.2307%, using four decimal places and not rounding up. Her husband dies when the NRB is £325,000. Transferable NRB = 69.2307% × £325,000 = £225,000, rounded up to the nearest pound at box 21. His combined NRB = £550,000.
Charitable gifts are also exempt from inheritance tax. If the first spouse left their entire estate to charity (rather than to the surviving partner), 100% of their NRB remains unused — a full transfer is still available.
Important: The calculation uses the NRB at the second death, not the first. If the NRB increases between the two deaths, the transferred amount is uplifted with it. The NRB is currently frozen at £325,000 until the end of the 2030 to 2031 tax year, so for now the transferred amount stays at the frozen figure.
HMRC requires evidence about the first spouse's estate to verify the percentage of NRB that was unused. Gather the following before completing IHT402:
The form lists three photocopies you must send with it:
Beyond the paperwork, the form says you need to know who benefited under the will or intestacy and what they received; whether jointly owned assets or assets in trust formed part of the first estate; and whether the first spouse made gifts or other chargeable transfers in the seven years before their death. One trap on the grant itself: HMRC's note says that “if the grant shows tax or duty as having been paid there will be no nil rate band available for transfer”.
If the first spouse died many years ago and records are hard to find, the form tells you to try the solicitor who acted for the estate, the executors or administrators, or other family members and close friends. It also points to the probate record and certificate services for England and Wales, Scotland and Northern Ireland.
The form runs to 23 numbered boxes across four pages. The ones that do the arithmetic are these:
Two historic quirks the notes flag, for very old first deaths. Where the first spouse died before 22 March 1972 there was no spouse exemption under estate duty at all, so everything passing under the will, intestacy or by survivorship goes in box 13. Where they died between 22 March 1972 and 12 November 1974 the spouse exemption was capped at £15,000, so only the excess over £15,000 that passed to the survivor goes in box 13.
IHT402 transfers only the standard nil rate band (NRB). If you also want to transfer unused Residence Nil Rate Band (RNRB) from the first spouse, you must complete IHT436 as a separate schedule alongside IHT435. These are entirely different forms for entirely different allowances, even though both relate to the spouse's unused tax-free bands.