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IHT400 Form: Complete Guide to Inheritance Tax Return UK 2026
By Farra Editorial Team•4 min read•Last updated: 15 October 2025
How do I complete the IHT400 form?
1The IHT400 is a 20-page inheritance tax return required when an estate exceeds £325,000 (or up to £500,000 if the residence nil-rate band applies), or when it does not qualify as an excepted estate.
2The form must be submitted to HMRC within 12 months of the end of the month in which the person died, and inheritance tax must be paid within six months of death or interest starts accruing.
4All asset values must be recorded at the date of death, not current market values — incorrect valuations are one of the most common causes of HMRC queries and penalties.
5Professional help from a solicitor or probate specialist typically costs £1,500–£5,000 and is deductible from the estate; most executors use professional help given the complexity of the form.
IHT400 is 20-page Inheritance Tax form required if estate exceeds £325,000 (or £500,000 with RNRB). Include supplementary schedules for property, shares, trusts, gifts. Takes 6-20 hours; most use solicitors (£1,500-£5,000). Submit within 12 months. Need valuations, bank statements, 7-year gift records. HMRC reviews all IHT400s—inaccurate valuations incur penalties.
When required: Estate over £325K (or £500K with RNRB), or complex estates
Form size: 20 pages main form plus schedules (varies by assets)
Time to complete: 6-20 hours (most use professional help £1,500-£5,000)
Deadline: Within 12 months of death
Documents needed: Valuations, bank statements, pension details, gift records
Common errors: Incorrect valuations, missing schedules, gift calculation mistakes
IHT400 Key Facts
• 20-page main form plus supplementary schedules
• Required if estate exceeds £325K (or £500K with RNRB)
• Takes 6-20 hours to complete
• Must submit within 12 months of death
• Most people use professional help due to complexity
1 in 3 probate applications are sent back. The most common reason: errors on exactly these forms.
Answer 5 questions in under 2 minutes. We'll tell you which forms apply to your estate, what goes in the fields people most often get wrong, and check your answers before you submit.
Which forms you need to file
The fields most likely to trigger a rejection
A pre-submission check so it goes through first time