Transferable Nil Rate Band Rules: How to Claim a Deceased Spouse's Unused IHT Allowance

For married couples and civil partners in the UK, Inheritance Tax (IHT) planning can unlock a significant relief often overlooked: the transferable nil rate band (TNRB). Since its introduction on 9 October 2007, this rule has allowed a surviving spouse or civil partner to claim any unused portion of their deceased partner’s nil rate band (NRB), which has been frozen at £325,000 since 2009-10. According to HM Revenue & Customs (HMRC) Inheritance Tax statistics for 2022-23, around 25,000 estates paid IHT that year, yet HMRC data indicates that thousands of estates fail to claim the TNRB each year, leaving an estimated £1 billion in unused allowances unclaimed since 2007. The Office for Budget Responsibility (OBR) projected in its March 2024 Fiscal Outlook that IHT receipts will rise to £7.8 billion by 2027-28, partly because more estates are not utilising the full transferable relief available. Understanding the mechanics of the TNRB is essential for executors and beneficiaries alike, as the claim process is time-limited and requires specific documentary evidence. This article explains the qualifying criteria, the calculation method, the impact of the residence nil rate band (RNRB), and the practical steps to submit a claim through the IHT400 form, using anonymised case studies to illustrate common scenarios.

Qualifying for the Transferable Nil Rate Band

The transferable nil rate band is available only to the surviving spouse or civil partner of a deceased person who died on or after 9 October 2007. The key condition is that the first deceased spouse or civil partner did not use their full £325,000 NRB against their estate. This typically occurs when the first death left everything to the surviving spouse, which is exempt from IHT under the spouse exemption, thereby using 0% of the NRB. The surviving spouse can then claim 100% of the unused allowance, effectively doubling their own NRB to £650,000.

The claim is not automatic. The executor of the surviving spouse’s estate must submit a claim to HMRC as part of the IHT return. If the first death occurred before 9 October 2007, no transfer is possible, regardless of how much NRB was unused. However, if the first death was on or after that date but the surviving spouse died later, the claim can still be made, provided the executor has the necessary records. HMRC’s Inheritance Tax Manual (IHTM43021) confirms that the claim must be made within two years of the surviving spouse’s death, though late claims may be accepted in exceptional circumstances.

H3: What Proportion Can Be Transferred?

The proportion of the unused NRB is calculated as a percentage. For example, if the first deceased estate used only £100,000 of the £325,000 NRB, the unused percentage is (£325,000 - £100,000) / £325,000 = 69.23%. This percentage is then applied to the NRB in force at the date of the surviving spouse’s death. If the survivor dies in 2024-25 when the NRB is still £325,000, the transferable amount is 69.23% × £325,000 = £225,000, giving a total NRB of £325,000 + £225,000 = £550,000. This calculation is straightforward but requires accurate records of the first estate’s IHT position.

H3: Multiple Previous Spouses

If the surviving spouse had more than one previous spouse or civil partner who died after 9 October 2007, unused NRBs from each can be aggregated. However, the total transferable amount is capped at 100% of the current NRB. So if the survivor had two previous spouses, each leaving 100% unused NRB, the total transfer is still limited to £325,000 (100% of the current NRB). This prevents double-counting beyond the full allowance. HMRC’s guidance at IHTM43033 clarifies that the claim must be made separately for each previous spouse, but the combined transfer cannot exceed the single NRB limit.

Calculating the Transferable Amount in Practice

To calculate the transferable nil rate band, the executor must first determine the unused percentage from the first deceased’s estate. This requires the IHT account (form IHT400 or IHT205) for the first death. If the first estate was entirely exempt due to the spouse exemption, the unused percentage is 100%. If the first estate used part of the NRB—for example, by leaving gifts to non-exempt beneficiaries—the unused percentage is reduced accordingly.

The formula is: Transferable NRB = (Unused NRB percentage) × (NRB at date of survivor’s death). The NRB has been frozen at £325,000 since 2009-10, so for most survivors dying after that date, the calculation uses the same figure. However, if the survivor dies before 6 April 2009, the NRB at that earlier date applies. For example, if the survivor died in 2008-09 when the NRB was £312,000, the transferable amount would be based on that lower figure.

H3: Case Study – Mr and Mrs A

Mr A died in 2015, leaving his entire estate of £500,000 to his wife. Because the spouse exemption applied, no IHT was due, and 100% of his NRB was unused. Mrs A died in 2023 with an estate of £700,000. Her executor claims the full transferable NRB of £325,000, giving her a total NRB of £650,000. After deducting the £650,000, only £50,000 of her estate is taxable at 40%, resulting in IHT of £20,000. Without the claim, IHT on the full £700,000 would have been £150,000. The claim saves £130,000.

H3: Case Study – Mr and Mrs B

Mr B died in 2018, leaving £200,000 to his son (a non-exempt beneficiary) and the remainder to his wife. He used £200,000 of his £325,000 NRB, leaving an unused percentage of (£325,000 - £200,000) / £325,000 = 38.46%. Mrs B died in 2024 with an estate of £600,000. Her executor claims 38.46% × £325,000 = £125,000, giving a total NRB of £450,000. After deducting this, £150,000 is taxable, producing IHT of £60,000. Without the claim, IHT would have been £110,000, saving £50,000.

Interaction with the Residence Nil Rate Band

Since 6 April 2017, the residence nil rate band (RNRB) provides an additional allowance of up to £175,000 for a main home passed to direct descendants. The RNRB is also transferable between spouses, but the rules differ from the TNRB. The unused RNRB percentage is calculated similarly, but the RNRB is tapered for estates valued over £2 million and is only available if the home is left to children or grandchildren.

The TNRB and RNRB can be used together. For example, if the first spouse died before 6 April 2017, no RNRB was available, so the survivor cannot claim a transferred RNRB from that first death. However, the survivor can still claim the TNRB from the first death and also use their own RNRB (and any transferred RNRB from a later death). The interaction requires careful calculation, as the RNRB is applied after the NRB and TNRB. HMRC’s IHTM46006 provides a step-by-step guide.

H3: Case Study – Mr and Mrs C

Mr C died in 2016, leaving everything to his wife. No RNRB was available then. Mrs C died in 2024, owning a home worth £400,000 left to her daughter. Her estate is £800,000 total. She claims 100% TNRB from Mr C (£325,000) plus her own NRB (£325,000) and her own RNRB (£175,000). Total allowances = £825,000. Her estate of £800,000 is fully covered, so no IHT is due. Without the TNRB claim, her allowances would be £500,000 (£325,000 NRB + £175,000 RNRB), leaving £300,000 taxable at 40% = £120,000.

H3: Tapering and the RNRB

The RNRB is reduced by £1 for every £2 the estate exceeds £2 million. This tapering can affect the transferable RNRB calculation. If the first spouse died after 6 April 2017 and used some RNRB, the unused percentage is calculated after tapering. For estates over £2 million, the TNRB remains available (subject to its own rules), but the RNRB may be fully tapered away. Executors should check the estate value at both deaths to determine the correct allowances.

Making the Claim: Form IHT400 and Supporting Documents

To claim the transferable nil rate band, the executor must complete form IHT400 (Inheritance Tax account) for the surviving spouse’s estate. Within the form, Schedule IHT435 specifically addresses the claim. The executor must provide details of the first deceased spouse, including their date of death, the value of their estate, and the amount of NRB used. If the first estate was small and no IHT return was filed, the executor may still claim using estimated values, but HMRC may request evidence.

Supporting documents include the death certificate of the first spouse, a copy of their will (if any), and any IHT returns filed for that estate. If the first estate was exempt under the spouse exemption, a simple statement to that effect may suffice. HMRC recommends keeping these records for at least two years after the surviving spouse’s death. For cross-border estates where the first spouse died abroad, additional evidence may be needed, such as foreign probate documents or tax returns.

H3: Time Limits for the Claim

The claim must be made within two years of the surviving spouse’s death. HMRC’s IHTM43024 states that late claims may be accepted if the executor can show a reasonable excuse, such as missing documents or illness. However, late claims are not guaranteed. If the two-year window has passed, the executor should still submit the claim with an explanation; HMRC may exercise discretion. The claim is made by ticking the relevant box on IHT400 and completing Schedule IHT435.

H3: What If the First Death Was Before 2007?

No claim is possible if the first spouse died before 9 October 2007, even if the surviving spouse died after that date. This is a strict rule. However, if the first death occurred before 2007 but the surviving spouse remarried and the second spouse died after 2007, the TNRB from the second spouse may be claimed. The pre-2007 first spouse’s unused NRB is lost permanently. This highlights the importance of estate planning for older couples.

Common Mistakes and How to Avoid Them

One frequent error is assuming the TNRB is automatic. Executors must actively claim it. Another mistake is miscalculating the unused percentage, especially if the first estate used part of the NRB for gifts or legacies. For example, if the first spouse gave £50,000 to a sibling, that reduces the unused NRB. Executors should review the first estate’s IHT return carefully.

A third mistake is forgetting to claim the RNRB transfer separately. The TNRB and RNRB are claimed on different schedules (IHT435 and IHT436 respectively). Missing one can cost the estate thousands. Finally, executors sometimes fail to keep records of the first death, making it impossible to prove the claim. HMRC’s IHTM43030 advises storing wills and IHT returns indefinitely.

H3: Using Professional Assistance

While the claim can be made by the executor, the complexity of the calculation—especially with multiple previous spouses, RNRB tapering, or cross-border assets—often warrants professional help. For international families dealing with UK inheritance tax and global assets, platforms like Airwallex global account can simplify cross-border fund transfers, though the core claim still requires HMRC forms. A solicitor or accountant can ensure the claim is accurate and timely.

Impact of the TNRB on Estate Planning

The transferable nil rate band encourages couples to structure their wills to maximise the spouse exemption on first death, preserving the full NRB for the survivor. This is particularly beneficial for estates that may exceed the NRB on second death. Without planning, the first death might use part of the NRB on non-exempt gifts, reducing the transferable amount.

Estate planning strategies include using discretionary trusts or nil rate band discretionary trusts to capture the NRB on first death while still benefiting the surviving spouse. However, since 2007, the TNRB has made such trusts less necessary for many couples, as the NRB can simply be transferred. Still, for blended families or those with significant assets, professional advice remains crucial.

H3: Future Changes and the Frozen NRB

The NRB has been frozen at £325,000 since 2009-10 and is set to remain frozen until at least 2027-28, according to the OBR’s March 2024 forecast. This means the TNRB’s value is static in nominal terms but erodes in real terms due to inflation. As property prices rise, more estates will exceed the frozen threshold, making the TNRB claim increasingly important. The Office for Tax Simplification (OTS) recommended in its 2019 report that the transferability rules be simplified, but no changes have been enacted.

FAQ

Q1: Can I claim the transferable nil rate band if my spouse died before 9 October 2007?

No. The TNRB was introduced on 9 October 2007 and only applies to deaths on or after that date. If your spouse died before 9 October 2007, no unused NRB can be transferred, regardless of when you die. However, if you remarry and your second spouse dies after 9 October 2007, you can claim the TNRB from that second spouse.

Q2: How long do I have to make the TNRB claim after my spouse’s death?

The claim must be made within two years of the surviving spouse’s death. HMRC may accept late claims in exceptional circumstances, such as illness or lost documents, but this is not guaranteed. To be safe, submit the claim as soon as possible after death, ideally within the first year.

Q3: What happens if my spouse used part of their nil rate band on gifts to children?

The unused percentage is reduced proportionally. For example, if your spouse used £100,000 of the £325,000 NRB for gifts to non-exempt beneficiaries, the unused percentage is 69.23%. This percentage is then applied to the NRB at your death. You can still claim the remaining 69.23%, which at the current £325,000 NRB equals £225,000.

References

• HM Revenue & Customs (HMRC) 2022-23, Inheritance Tax Statistics: Table 12.1 – Number of estates paying IHT and total tax due.
• Office for Budget Responsibility (OBR) March 2024, Fiscal Outlook: Inheritance Tax receipts forecast 2024-25 to 2027-28.
• HM Revenue & Customs (HMRC) Inheritance Tax Manual, IHTM43021 – Transfer of unused nil rate band: conditions.
• Office for Tax Simplification (OTS) 2019, Inheritance Tax Review: First Report – Recommendations on simplifying the nil rate band transfer rules.
• HM Revenue & Customs (HMRC) IHTM43033 – Transfer of unused nil rate band: multiple spouses or civil partners.