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IHT436 is the counterpart to IHT402: just as IHT402 transfers the unused standard nil rate band from a deceased spouse, IHT436 transfers the unused Residence Nil Rate Band. When both apply, a couple can potentially shelter up to £1,000,000 from inheritance tax entirely — but only if the conditions are met and both forms are correctly completed.
IHT436 is the supplementary schedule used to transfer the unused Residence Nil Rate Band (RNRB) from a first-deceased spouse or civil partner to the estate of the surviving partner. It is submitted alongside IHT435 (which claims the RNRB on the current estate) and the main IHT400.
The principle is the same as the transferable nil rate band (IHT402): allowances that were unused at the first death are not lost — they can be transferred and applied at the second death. This is sometimes called the transferable RNRB (TRNRB).
Like IHT402, the transfer is expressed as a percentageof the RNRB, not a fixed amount — and that percentage is applied to the RNRB in force at the second death.
IHT436 carries a deadline printed on its own front page: “You must send this form to us no later than 24 months after the end of the month in which the deceased died.” The form’s worked example: a death on 10 October 2007 gives a deadline of 31 October 2009.
The underlying rule is section 8L of the Inheritance Tax Act 1984, and HMRC’s manual (IHTM46042) adds two things worth knowing. The personal representatives get the later of that 24 months and three months beginning with the date they first started to act. And if they do not claim in time, anyone else liable for the tax can claim within such later period as an HMRC officer allows — so a missed deadline is not automatically the end of it, but it is no longer a claim you can simply make.
You need to complete IHT436 when all of the following apply:
Critical point: IHT436 cannot be submitted alone. It is always an addition to IHT435. If the current estate does not qualify for the RNRB at all (for example, because there is no qualifying property), you cannot claim the transferred RNRB either — it can only be used to top up an existing IHT435 claim.
The RNRB was introduced on 6 April 2017. Before that date, it did not exist — so it was impossible for anyone to have used their RNRB.
The legislation deals with this by deeming: where the first spouse died before 6 April 2017, the form’s notes say the Residential Enhancement at that time “is deemed to have been £100,000”, and the taper threshold deemed to have been £2 million. It does not matter what they owned, how their estate was distributed, or whether they owned a property at all — none of that can have used up an allowance that did not exist.
There is one thing that still bites, and it is the reason questions 7 to 13 exist. If the first spouse’s estate was worth more than the £2 million taper threshold, the deemed allowance tapers away in the usual £1-for-£2 way, and the percentage you carry forward is less than 100%. Question 7 asks for the total net value of their estate before exemptions or reliefs, and question 8 for the taper threshold at their death: if question 7 is less than question 8 you enter 100.0000% and skip on; if it is more, you work the taper through. So “died before 2017” means 100% unless their estate was over £2 million.
Example: John died in 1995. His wife Mary dies in 2026 and qualifies for the RNRB on her estate. She can claim 100% of the £175,000 RNRB via IHT436 in addition to her own £175,000 RNRB via IHT435 — giving a combined RNRB of £350,000, despite the fact the RNRB did not exist when John died.
Where the first spouse died after 6 April 2017, you need to calculate what percentage of their RNRB was unused:
Susan died in 2020 when the RNRB was £175,000. She left her entire estate to her husband (spouse exemption applied), so she used no RNRB. Percentage unused: 100%. Her husband dies in 2026 when the RNRB is £175,000. Transferable RNRB = 100% × £175,000 = £175,000.
Peter died in 2019 when the RNRB was £150,000. He left a property worth £90,000 to his children (using £90,000 of RNRB) and the rest to his wife. Percentage unused: (£150,000 − £90,000) ÷ £150,000 = 40%. His wife dies in 2026 when the RNRB is £175,000. Transferable RNRB = 40% × £175,000 = £70,000.
To support the IHT436 claim, you will need:
The £2 million taper that applies to the RNRB (see the IHT435 guide) applies to the combined RNRB — own RNRB plus transferred RNRB from IHT436. There is no relaxation of the taper threshold because a transferable RNRB is being claimed.
For a couple claiming both their RNRBs (total RNRB of £350,000), the taper means:
Note: The taper withdrawal rate of £1 per £2 above £2 million applies to the total RNRB available. For a couple with a combined RNRB of £350,000, full withdrawal occurs at a net estate of £2,700,000 (£2m + 2 × £350,000).
Where both the standard NRB and the RNRB are being transferred from a first deceased spouse, you submit IHT402 (for the NRB transfer) and IHT436 (for the RNRB transfer) alongside the IHT400 and IHT435. These are separate forms for separate allowances and must both be completed. Together, they can give a combined tax-free allowance of up to £1,000,000: two NRBs (£650,000) plus two RNRBs (£350,000).
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