Post a ten-year anniversary return to HMRC next week on the form your firm used last time, and it will come back unprocessed. HMRC stops handling old Inheritance Tax 100 forms after today, 31 August 2026. From tomorrow, anything filed on a previous version gets returned with a request to submit again on the current one, and the six-month clock on the underlying charge carries on running while the paperwork travels.
TL;DR: HMRC will not accept old IHT100 forms submitted after 31 August 2026. The single IHT100 was replaced in August 2024 by event-specific forms IHT100a to IHT100h, each with the tax calculation built in. Trust ten-year and exit charges must be reported and paid within six months of the end of the month the event fell in. Late accounts start at a £100 penalty.
What Changed on 31 August 2026
HMRC has withdrawn the grace period for earlier versions of the IHT100. The wording is blunt: "If you submit previous versions of these forms after 31 August 2026 they will not be accepted and you will be asked to resubmit the correct version" (GOV.UK Agent Update issue 144, 2026).
The forms themselves are not new. HMRC retired the single IHT100 and its IHT100WS worksheet on 12 August 2024, replacing them with a set of accounts built around the event being reported (STEP, 2024). What ended today is tolerance for the old paperwork.
It catches anyone reporting a chargeable event: trustees handling a ten-year anniversary or an exit, people who have made a gift with tax payable immediately, and agents filing on their behalf. The real exposure is the calendar rather than the stationery. HMRC asks for the correct version to be resubmitted, and nothing in that process pauses the statutory deadline, so a return posted comfortably inside it can still finish up late.
Which IHT100 Form Do You Actually Need?
Match the form to the event, then attach only the schedules that apply. There is no longer a general IHT100 to file alongside the event form.
| Chargeable event | Form |
|---|---|
| Gift with tax payable immediately | IHT100a |
| Interest in possession ending in lifetime | IHT100b |
| Interest in possession ending on death | IHT100b (death) |
| Assets leaving a trust (exit charge) | IHT100c |
| Ten-year anniversary charge | IHT100d |
| Charges on special trusts | IHT100e |
| Conditional exemption ceasing | IHT100f |
| Assets formerly in an 18-to-25 trust | IHT100h |
Supplementary schedules run from D31 to D39 and cover foreign assets, life policies, business relief, quoted shares and the rest. Each event form now carries the calculation that used to sit on the separate worksheet (GOV.UK Inheritance Tax account (IHT100), 2026).
When Is the Form Due, and When Is the Tax Due?
For relevant property trust charges, the same day. Trustees get six months from the end of the month in which the chargeable event happened, both to deliver the account and to pay. Finance Act 2014 aligned the two dates, amending sections 216 and 226 of the Inheritance Tax Act 1984 for charges arising on or after 6 April 2014 (legislation.gov.uk, 2014).
A ten-year anniversary falling on 14 October 2026 therefore runs to 30 April 2027 for the account and the payment.
One step trustees routinely underestimate: you need an Inheritance Tax reference before you can pay, applied for on form IHT122, and HMRC asks for at least three weeks' notice (GOV.UK form IHT122, 2026). Start that in the final fortnight and the payment misses the date even though the money was sitting ready.
Why More Business Owners Will Meet This Form From April 2026
Trusts holding trading company shares used to have very little to report. Business property relief at 100% took the value out of charge, so ten-year anniversaries came and went quietly. That stopped being automatic on 6 April 2026.
A £2.5 million allowance now covers the combined value of property qualifying for 100% agricultural or business relief, with relief dropping to 50% above it. The government raised the cap from the £1 million first announced, confirming the higher figure on 23 December 2025 (Saffery, 2025).
Relevant property trusts get their own allowance and it refreshes at each ten-year anniversary. Above it, half the excess falls into charge, so the effective ten-year rate tops out at 3% against the headline 6%. Trusts settled before 30 October 2024 keep unlimited relief on exits until their first anniversary on or after 6 April 2026, then join the new regime (HMRC Inheritance Tax Manual IHTM25551, 2026). If your company shares sit in a family trust, this is worth pairing with our note on what changes for pensions and inheritance tax in April 2027.
Do You Have to File at All?
Sometimes not. A settlement can qualify as an excepted settlement, and then no account is due. The central test at a ten-year anniversary is that the chargeable value does not exceed 80% of the nil rate band, which is £260,000 while the band stands at £325,000. Other conditions sit alongside it, including UK-resident trustees throughout and no related settlements (The Inheritance Tax (Delivery of Accounts) (Excepted Settlements) Regulations 2008).
That £260,000 line is fixed for a while. The nil rate band is frozen at £325,000 until April 2031 after the Autumn Budget 2025 extension, and inheritance tax receipts reached a record £8.5 billion in 2025-26, the fifth consecutive annual high (Professional Adviser, 2026). In our experience this is exactly where trustees get caught: the trust was comfortably excepted in 2016, is not in 2026, and nobody re-ran the test in between.
What Happens If You File Late or Send the Wrong Version?
Section 245 of the Inheritance Tax Act 1984 sets an initial £100 penalty for failing to deliver an account, a further £100 once it is six months late, and up to £3,000 where it runs past a year. Penalties are capped at the tax due, which is little comfort on a trust with a genuine charge, and interest on unpaid tax runs separately.
What we see most often is a trust that met its deadline on paper and missed it in practice, because the form went back and forth before HMRC ever logged it. If penalties are already in play, our guide to HMRC late payment penalties covers how the interest and surcharges stack up.
Anyone reviewing trust exposure ahead of the Autumn Budget on 28 October should treat the reporting position as part of that review, not a separate job for the accounts team.
Frequently Asked Questions
Where do I get the current IHT100 forms?
From the Inheritance Tax account (IHT100) collection on GOV.UK, downloaded fresh. A PDF saved to your document system in 2023 is a previous version and will be rejected from 1 September 2026, even if the layout looks familiar.
Can I file an IHT100 online?
No. The IHT100 suite is printed and posted to HMRC Inheritance Tax, BX9 1HT. Send it tracked and keep proof of postage, because the delivery date matters when a six-month statutory deadline is involved.
I posted an old form in August. Is it safe?
Forms submitted on or before 31 August 2026 are still processed. The cut-off applies to submission rather than to when HMRC opens the envelope, so proof of postage from August protects you.
If business relief covers everything, does the trust still file?
Possibly. One question clients always ask is whether full relief removes the filing duty, and on its own it does not. Filing turns on the excepted settlement conditions and the chargeable value, so a trust can owe no tax and still owe a form.
Which form covers a ten-year anniversary charge?
IHT100d, together with whichever of schedules D31 to D39 fit the trust's assets. The calculation is built into the form, so the old IHT100WS worksheet is no longer needed.
If you act as trustee for a family trust with a ten-year anniversary or an exit charge coming up, get in touch. We will check which event form applies, whether the settlement still qualifies as excepted, and what the new £2.5 million relief allowance does to the numbers. You can also see the full range of our tax and advisory services.