- What the residence nil rate band does
- The rule people get wrong: it's a percentage
- The Residential Enhancement by year
- The £2 million taper
- Working through the form
- Who counts as a direct descendant
- When the home counts as inherited
- The order of the calculation on the second death
- Before you send it
- The verdict
- Frequently asked questions
IHT436 is the HMRC form for claiming a late spouse's or civil partner's unused residence nil rate band (RNRB) on the estate of the second person to die. It's used with form IHT435, which claims the RNRB itself, when the first spouse died before 6 April 2017 or died later without using all of their RNRB. It has to reach HMRC within 24 months of the end of the month of the second death.
This page uses the IHT436 form and notes (HMRC 08/22) and HMRC's residence nil rate band guidance, as of October 2026.
What the residence nil rate band does
The RNRB is an extra tax-free allowance when a home, or a share of one, passes to direct descendants. GOV.UK explains that leaving your home to children, including adopted, foster or stepchildren, or grandchildren, can raise the threshold to £500,000, as long as the estate is worth less than £2 million. Any unused threshold can pass to a surviving spouse or civil partner, and IHT436 is how the residence part is claimed.
The rule people get wrong: it's a percentage
The form's own notes say it's the unused percentage of the RNRB that transfers, not the unused amount. You work out what share of the first spouse's RNRB went unused, then apply that percentage to the RNRB in force when the second person dies. Where the first death was before 6 April 2017, nothing could have been used, so the full 100% is available to transfer.
The Residential Enhancement by year
| Tax year | Residential Enhancement |
|---|---|
| To 5 April 2018 | £100,000 |
| 2018 to 2019 | £125,000 |
| 2019 to 2020 | £150,000 |
| 2020 to 2026 | £175,000 |
If the first spouse died before 6 April 2017, the form treats the Residential Enhancement at that time as £100,000. All figures are as of October 2026.
The £2 million taper
The RNRB tapers away for estates over £2 million, even if a home goes to direct descendants: it drops by £1 for every £2 above the threshold. The taper threshold was £2 million from 6 April 2017 to 5 April 2026, and is treated as £2 million for deaths before 6 April 2017. Tapering on the first estate also cuts what's left to transfer.
Working through the form
| If the first spouse | Answer | What you calculate |
|---|---|---|
| Used no RNRB (including all deaths up to 5 April 2017) | Questions 7 to 15 | Their net estate against the taper threshold, any taper, the unused RNRB and the unused percentage to 4 decimal places |
| Used some RNRB | Questions 16 to 22 | Their Default or Adjusted Allowance, the RNRB used, and the unused percentage to 4 decimal places |
Either route ends by multiplying the current Residential Enhancement by the unused percentage, which gives the amount available to transfer. HMRC's residence nil rate band calculator then works out the full entitlement on the second death.
Who counts as a direct descendant
- Children, grandchildren, great-grandchildren and great-great-grandchildren.
- Stepchildren, adopted children and foster children treated as the person's child.
- Children the person was guardian or special guardian for when the child was under 18.
- The spouse or civil partner of any of these, including a widow, widower or surviving partner who hadn't remarried before the death.
Nephews, nieces, siblings and other relatives don't count. A child doesn't have to be under 18 at the date of death.
When the home counts as inherited
The RNRB on the second estate still depends on the home passing to direct descendants, and HMRC's guidance sets out how that works:
- The home can pass by will, under the rules of intestacy or by other legal means, and doesn't have to be named in the will; it can come through the residue.
- The descendants must become entitled when the person dies. A will that makes grandchildren wait until a certain age puts the home in trust, and the RNRB won't apply.
- The executor can sell the home during the administration and pass on the proceeds, and the RNRB is still available.
- A deed of variation that leaves the home to direct descendants counts, because HMRC looks at the outcome of the deed rather than the original wording.
The guidance also covers downsizing: the calculator works out the RNRB if the person downsized or sold their home. If the home is worth less than the maximum RNRB, the shortfall can't be set against other assets, but it can be available to transfer to the spouse's or civil partner's estate.
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The order of the calculation on the second death
- Add any transferred RNRB from IHT436 to the RNRB due on the estate, giving a combined residence nil rate band.
- Take the combined RNRB off the value of the estate.
- Take off the basic threshold and any transferred basic threshold from what's left.
HMRC notes that the order usually makes no difference, but in some cases it affects how much unused threshold is left to pass on.
Before you send it
- Get the first spouse's death date, marriage details and Inheritance Tax reference.
- Find out whether any RNRB was used on their estate; if it was, the figures should be on their Inheritance Tax return.
- Complete IHT435 for the estate you're dealing with now.
- Send IHT436 to HMRC in time. The form's example: a first death on 15 May 2006 and a second on 10 October 2007 meant a deadline of 31 October 2009.
The unused ordinary nil rate band from the first death is a separate claim, made on IHT402. Many second estates with a home going to children need both claims. Both go in with the IHT400.
The verdict
IHT436 is worth the arithmetic. Because the unused percentage carries forward, an older first death can pass on a full 100% that's applied to today's higher Residential Enhancement. Gather the first spouse's papers early, check the £2 million taper on both estates, and send IHT436 with IHT435 well inside the 24 months.
Frequently asked questions
What is IHT436?
It's the form used to claim transferable residence nil rate band from a spouse or civil partner who died before the deceased.
When is IHT436 due?
No later than 24 months after the end of the month in which the deceased died.
Is the unused residence nil rate band transferred as an amount or a percentage?
As a percentage. The form's notes say it's the unused percentage of the RNRB that's transferred, not the unused amount.
What if the first spouse died before April 2017?
Their estate couldn't have used any RNRB, so you complete questions 7 to 15 and treat the Residential Enhancement at that time as £100,000.
Do I need IHT435 as well as IHT436?
Yes. IHT436 is completed when you're claiming RNRB on the estate, which needs form IHT435 too.
