HMRC Stops Accepting Old IHT100 Forms After 31 August 2026

HM Revenue & Customs confirmed in Agent Update issue 144 that it will stop processing old Inheritance Tax 100 forms (IHT100) after 31 August 2026. If you submit a previous version after that date, HMRC will not accept it and will ask you to resubmit on the correct, current form.

The change was first signalled in the HMRC Trusts and Estates newsletter in August 2024. With one month left from early August 2026, personal representatives, trustees, and agents still using archived PDFs or outdated practice templates need to switch before filings stall.

The deadline is about form versions, not about Inheritance Tax rates or reliefs. You still use IHT100 (and related schedules) to tell HMRC that Inheritance Tax is due where the estate or trust position requires it. What changes is that superseded form editions leave HMRC’s processing stack after 31 August 2026.

Agent Update 144’s practical instruction is simple: switch to the latest forms as soon as possible and use those current forms to inform HMRC that Inheritance Tax is due. Keeping a local copy of an old IHT100 from a previous estate is a common source of accidental resubmissions — purge those templates from shared drives and practice management systems.

Download the current IHT100 pack and schedules from GOV.UK rather than reusing a file saved from an earlier matter. Confirm your case-management software or document assembly tool has been updated to the edition HMRC currently publishes.

Diary any estates where you expect to file in September 2026 or later and verify the pack version before you start compiling valuations. If a draft return was prepared on an old form earlier in 2026, rebuild it on the current edition before submission — do not assume a half-completed old pack can be patched.

Coordinate with probate solicitors and valuers so supporting schedules match the field layout of the current forms. Version mismatches often surface only when HMRC rejects the pack, costing weeks at a sensitive time for families.

Clean asset registers, bank statements, and property valuations remain the backbone of an accurate Inheritance Tax account — regardless of which IHT100 edition you use. FinnAccountings helps UK and Irish families and advisers organise bookkeeping trails and tax prep drafts with Chartered Accountant insight before you or your qualified adviser completes HMRC or Revenue filings. Start a free trial if you need review-ready document packs — we do not submit IHT100 forms to HMRC on your behalf.

For related UK compliance context this summer, see our tax adviser registration deadline briefing (first MMTAR tranche closes 18 August 2026) and the free tax calculator for illustrative estimates only.