How do I get the unique code?

HMRC issues it to the person who submitted the IHT400, by letter, once the account has been processed and any tax due has been paid.

Forms · 4 min read

IHT421: the probate summary and the unique code

IHT421 is the link between HMRC and HMCTS. Until the probate registry has confirmation from HMRC, no grant can be issued on a taxable estate.

Written and reviewed by Ramani Gill, Founder & CEO — Solicitor, TEP, BA, LLM. Last reviewed 2026-08-19.

The role it plays

You submit the IHT400 and pay the tax due
HMRC processes the account and confirms the values
HMRC issues a unique code, or in some cases a stamped IHT421, to the applicant
You quote that code on the probate application
HMCTS can then issue the grant

Do not apply before the code arrives

Submitting the probate application without HMRC's confirmation gets it stopped and put back in the queue. Allow around twenty working days after payment.

If the values change

Where you discover an error after submitting the IHT400, correct it with HMRC using form C4 before or after the grant. The probate registry will work from HMRC's confirmed figures.

Doing this yourself?

Our guided service walks an executor through valuations, the HMCTS forms and the estate accounts for a one-off £349.

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Excepted estates do not use it

If the estate is excepted, there is no IHT400 and no IHT421. You give summary values directly on the probate application and go straight to HMCTS.

GOV.UK — Form IHT421

Common questions

How do I get the unique code?: HMRC issues it to the person who submitted the IHT400, by letter, once the account has been processed and any tax due has been paid.

Not sure whether this estate is straightforward?

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