Executors need an inheritance tax reference number before they can pay any inheritance tax, and before they send an IHT400 on which tax is due. HMRC asks for the application at least three weeks ahead. It is made online with a GOV.UK sign in or an email address, and no reference is needed if there is no tax to pay.

When do executors need a reference number?

The trigger is tax, not paperwork. HMRC’s IHT400 notes (box 3) say that if there is any inheritance tax to pay you need a reference number before you send the IHT400, and that you do not need to apply for one, or complete that box, if there is no tax to pay. GOV.UK’s guide to paying the bill says the same from the other direction: you need a payment reference number before you can pay.

So the reference is not needed for an excepted estate, and it is not needed where a full IHT400 is required but no tax arises, for example where everything above the nil rate band passes to a spouse. It is needed whenever there is tax on the estate, including where only part of it will be paid before the grant.

How do you apply?

The form is called “Apply for an Inheritance Tax reference (IHT422)”, and the GOV.UK page for it now links to an online service rather than a paper form. You apply using either GOV.UK sign in details, which you can create if you do not have them, or simply an email address. The IHT400 notes still mention the option of posting a paper Schedule IHT422, but the current publication page offers the online route, so that is the one to use.

Have the deceased’s full name, last address and date of death to hand. The same details appear next to the reference on later forms, such as the IHT423 that each bank receives under the Direct Payment Scheme, so it helps if they match exactly.

How long does it take?

The guidance does not give a processing time for the reference itself. What it does say, in both the IHT400 notes and the GOV.UK paying guidance, is that you should apply at least three weeks before you plan to send the IHT400 or make a payment. Treat three weeks as the minimum planning gap, not a guarantee.

The reference is only the first wait. Once HMRC has the IHT400 and the payment, GOV.UK says the unique code needed to apply for probate in England and Wales (or confirmation in Scotland) usually arrives within 20 working days of HMRC receiving the IHT400 or the payment, whichever is later. In Northern Ireland HMRC returns a completed IHT421 on the same timescale. A realistic plan therefore allows roughly two months from applying for the reference to holding the code.

Timing also affects interest. Inheritance tax is due by the end of the sixth month after the month of death, and HMRC charges interest on anything paid later; see HMRC late payment interest. Because you cannot pay without a reference, a late application can mean interest that could have been avoided.

Is there a different form for trusts and lifetime gifts?

Yes. Trustees and people reporting chargeable events on the IHT100 series use form IHT122, “Application for an Inheritance Tax reference following a chargeable event”. GOV.UK describes it as the form to use if you owe inheritance tax on a trust or lifetime transfer. Unlike the estate application it is completed on screen, then printed and posted to HMRC Inheritance Tax at BX9 1HT, and the reference should again be requested at least three weeks before payment.

The IHT122 has three alternative sections. Section 1 covers the person who has died, used where an IHT100a reports potentially exempt transfers that have become chargeable on death or an IHT100b(death) reports the end of a qualifying interest in possession. Section 2 covers a living transferor, and section 3 the settlor of a trust. HMRC warns that if every detail asked for is not filled in, it may not be able to allocate a reference.

Where is the reference used once you have it?

  • The IHT400. It goes in box 3 on page 1.
  • Every payment. For a cheque, GOV.UK says to write the deceased’s name and the payment reference number on the back. A wrong reference can delay the payment or see it used against a different tax bill.
  • The Direct Payment Scheme. Each IHT423 sent to a bank, building society, NS&I or broker carries the reference, and the form warns that the payment cannot be matched to the account without a valid one. See paying IHT from the deceased’s bank account.
  • Payments on account. The IHT400 notes say you must give the reference when paying, and that HMRC will not charge interest on an amount paid on account from the date it is received.
  • A grant on credit. The letter asking HMRC to postpone payment must have “Grants on credit” and the reference at the top.
  • Later schedules and corrections. The IHT403 gifts schedule asks for the reference if known, and a corrective account will quote it too.

HMRC does not send a receipt for each payment. GOV.UK says it will write when all the tax and interest has been paid, so executors paying from their own account should keep their bank statements as evidence.

How might the timetable look?

Illustration only. Ruth dies on 10 February 2026. Her estate will owe tax, so her executors need a reference. Tax is due by 31 August 2026, the end of the sixth month after the month of death, and the IHT400 itself must be delivered within 12 months from the end of the month of death, by 28 February 2027.

  1. Mid May 2026: the executors apply online for the reference while valuations are still coming in.
  2. Early June: with the reference received, they complete the IHT400 and send IHT423 forms to the deceased’s bank and broker at the same time as the IHT400 goes to HMRC.
  3. 22 June: the last of the direct payments reaches HMRC.
  4. About 20 July: the probate code arrives, 20 working days after the later of the IHT400 and the payment.

Had they waited to apply until the IHT400 was finished in early June, the same steps would have run three weeks later. Every week of delay pushes the probate application back, and if the tax slips past 31 August, interest starts to run.

What mistakes cause delay?

  • Applying only once the IHT400 is complete, rather than as soon as it is clear tax will be due.
  • Quoting the deceased’s Unique Taxpayer Reference or another HMRC number on a payment instead of the inheritance tax reference.
  • Enclosing a cheque with the IHT400 or other papers. The update notes on HMRC’s reference forms say cheques should be sent separately from any forms or letters.
  • Applying for an estate reference when the charge is on a trust or a lifetime transfer, which needs the IHT122.
  • Applying when no tax is payable at all, which wastes time and is not needed.

The rest of the process is covered in completing the IHT400 and paying inheritance tax before probate.

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Reviewed by Christine Anderson, Broker, Solar Protect. Last reviewed 19 October 2026. Part of Accountapedia, the Solar Protect guide to UK tax and accounting. This page is general information, not personalised advice.