UK Borderline Excepted Estates 2026/27 — IHT400 or Probate?

An estate can be non-taxpaying without automatically being an excepted estate. The distinction matters because an excepted estate may be able to apply for probate or confirmation without first submitting a full IHT400 account, while an estate that fails the excepted-estate conditions may need to report to HMRC even if the final Inheritance Tax bill is nil.

HMRC’s August 2026 Agent Update specifically warned advisers about borderline cases. The most important practical point is that you must not simply add the residence nil rate band (RNRB) or a transferable nil rate band to the threshold when deciding whether an estate qualifies as excepted. Those allowances may need to be claimed through an IHT400 and supporting schedules.

For the broader tax calculation, see the UK Inheritance Tax 2026/27 guide. For the payment reference workflow where IHT is due, see the IHT422 reference-number guide.

What is an excepted estate?

An excepted estate is an estate that meets specific conditions allowing the personal representatives to use a simplified probate or confirmation reporting route. HMRC’s manual identifies categories including low-value estates, exempt estates and certain estates involving people who are not long-term UK resident under the post-6 April 2025 rules.

The conditions are not just a comparison between the gross estate and the headline nil rate band. The relevant test can involve the gross value, debts, spouse or civil-partner exemption, charity exemption, lifetime transfers, the deceased’s residence status and whether a transferable allowance is being claimed.

The exact test can also depend on the date of death and, for some timing rules, the date the grant of representation is applied for. Use the current HMRC manual and IHT forms for the applicable dates rather than copying a threshold from an older estate file.

Why borderline estates are risky

The simplified route is designed for straightforward cases. A borderline estate may look non-taxpaying after applying every possible allowance, but the allowance may not be available for the simplified test or may require a formal claim and supporting evidence.

HMRC’s Agent Update warns in particular that:

• the residence nil rate band should not be used automatically when deciding whether an estate is excepted;
• a transferable or brought-forward allowance should not be treated as automatic;
• downsizing and transferable allowances may need to be claimed in an IHT400; and
• failing to submit an IHT400 when required can create later calculation, evidence and deadline problems.

This is why “the estate is below £1 million after allowances” is not a sufficient decision rule. It may be a useful planning observation, but it does not replace the legal excepted-estate conditions.

RNRB is not an automatic excepted-estate uplift

The RNRB can apply when a qualifying home passes to direct descendants, and unused RNRB may in some cases transfer from a spouse or civil partner. Those are substantive Inheritance Tax rules. The estate still needs to satisfy the separate conditions for the reporting route it wants to use.

Where the estate needs to claim RNRB or transferred RNRB, supporting information may be required through the IHT400 and the relevant schedules. A personal representative should not omit a full account merely because the final tax calculation appears to fall below zero after a possible RNRB claim.

Check the ownership, beneficiary, home value, downsizing history and transferred percentage. If any of those facts are uncertain, treat the case as requiring professional review before selecting an excepted-estate route.

Transferable nil rate band needs the same caution

The transferable nil rate band can increase the threshold available to a surviving spouse or civil partner’s estate where the conditions are met. But the transfer is a claim with evidence requirements, not a blanket uplift that can be assumed from the fact that the first spouse left everything to the survivor.

Lifetime gifts, chargeable transfers, the first death’s estate and the proportion of the nil rate band used all matter. HMRC’s manual contains specific conditions for when a transferable nil rate band can be considered within the excepted-estate rules. If those conditions are not met, the personal representatives may need to submit an IHT400 and claim the transfer formally.

When should you consider IHT400?

Consider the full IHT400 route when the estate is not clearly within an excepted category, when a relief or transferred allowance needs a formal claim, or when the estate includes facts outside the simplified conditions. Examples can include complex lifetime gifts, significant trusts, uncertain residence status, a claim to transferable allowances or assets whose valuation is disputed.

Submitting an IHT400 is not the same as admitting that tax is payable. It is the detailed account used to report the estate and support the calculation. The relevant form, schedules and evidence depend on the estate, and HMRC’s current instructions take precedence over a generic checklist.

If IHT is due, the reference-number workflow is separate: use the current IHT422 process and allow the time HMRC specifies before payment. Do not confuse the reporting decision with the payment-reference decision.

A borderline-estate review checklist

Frequently Asked Questions

Evidence and decision checks

A reliable uk borderline excepted estates 2026 27 review starts by fixing the tax year and the date on which the relevant event happened. Record the person's or business's status, the income or transaction category, the amount before tax, tax already withheld, and any election or claim being relied on. Do not combine a headline figure with a final liability: the result can change when another income source, a payment date, an ownership interest or a qualifying condition is added.

Keep the source documents behind every important input. Depending on the subject, that may include payslips, invoices, bank statements, contracts, provider statements, travel records, HMRC notices, payroll submissions, valuations or correspondence. Where an amount is apportioned, write down the method and retain the underlying total. If a correction is made, preserve the original figure and explain the reason, date and evidence for the replacement.

Before relying on the result, check the current official guidance for the same tax year and jurisdiction. Distinguish enacted law from a consultation, draft measure, announcement or future proposal, and record the effective date. Reconcile the final estimate to the relevant return, payroll record or HMRC account. A calculator or explanatory guide can support a decision, but it cannot replace the eligibility test or the official filing and payment process.

Evidence and decision checks

A reliable uk borderline excepted estates 2026 27 review starts by fixing the tax year and the date on which the relevant event happened. Record the person's or business's status, the income or transaction category, the amount before tax, tax already withheld, and any election or claim being relied on. Do not combine a headline figure with a final liability: the result can change when another income source, a payment date, an ownership interest or a qualifying condition is added.

Keep the source documents behind every important input. Depending on the subject, that may include payslips, invoices, bank statements, contracts, provider statements, travel records, HMRC notices, payroll submissions, valuations or correspondence. Where an amount is apportioned, write down the method and retain the underlying total. If a correction is made, preserve the original figure and explain the reason, date and evidence for the replacement.

Before relying on the result, check the current official guidance for the same tax year and jurisdiction. Distinguish enacted law from a consultation, draft measure, announcement or future proposal, and record the effective date. Reconcile the final estimate to the relevant return, payroll record or HMRC account. A calculator or explanatory guide can support a decision, but it cannot replace the eligibility test or the official filing and payment process.

Evidence and decision checks

A reliable uk borderline excepted estates 2026 27 review starts by fixing the tax year and the date on which the relevant event happened. Record the person's or business's status, the income or transaction category, the amount before tax, tax already withheld, and any election or claim being relied on. Do not combine a headline figure with a final liability: the result can change when another income source, a payment date, an ownership interest or a qualifying condition is added.

Keep the source documents behind every important input. Depending on the subject, that may include payslips, invoices, bank statements, contracts, provider statements, travel records, HMRC notices, payroll submissions, valuations or correspondence. Where an amount is apportioned, write down the method and retain the underlying total. If a correction is made, preserve the original figure and explain the reason, date and evidence for the replacement.

Before relying on the result, check the current official guidance for the same tax year and jurisdiction. Distinguish enacted law from a consultation, draft measure, announcement or future proposal, and record the effective date. Reconcile the final estimate to the relevant return, payroll record or HMRC account. A calculator or explanatory guide can support a decision, but it cannot replace the eligibility test or the official filing and payment process.

Read HMRC’s borderline excepted-estate warning, the rules about excepted estates and the transferable nil rate band conditions. For the broader tax position, use the Inheritance Tax guide, and for an IHT payment reference use the IHT422 guide.

Official sources

• HMRC — Agent Update 146: borderline excepted estates
• HMRC Inheritance Tax Manual — rules about excepted estates
• HMRC Inheritance Tax Manual — transferable nil rate band and excepted estates
• HMRC — IHT400 Notes, April 2026 edition