Start with the estate facts, not the form number

Executors often start by asking which inheritance tax form they need. In practice, the better starting point is:

what the estate is worth
what it consists of
whether there are gifts, trusts, or relief claims to review
whether the estate falls into an excepted route or needs fuller reporting

The form choice comes after that analysis, not before it.

A sensible assessment route

build the asset and liability picture using date-of-death values
check whether anything in the estate makes the tax position less straightforward
review gifts, trusts, reliefs, exemptions, and any spouse or civil-partner transfer issues
decide whether the estate is likely to be excepted or whether the full IHT400 route is needed
record the evidence behind that decision so it can be explained later

This is the stage where shortcuts create later risk.

What usually pushes an estate into fuller reporting

An estate is more likely to need fuller inheritance tax reporting where there are issues such as:

a higher-value estate
lifetime gifts that need to be reviewed
trusts or settled property
relief claims that depend on supporting evidence
foreign or more complex assets
uncertainty over available nil-rate band or residence nil-rate band claims

The more moving parts there are, the less sensible it is to assume the simplest route will apply.

The IHT400 route

The IHT400 route is used for estates that need the fuller inheritance tax account and, where relevant, supporting schedules.

This is usually the route where:

the estate is not excepted
additional supporting schedules are needed for particular asset or tax issues
the tax analysis needs to be set out in more detail

If the estate is moving down this route, the important point is not just the main form name. It is making sure the supporting schedules and evidence match the estate facts.

A note on the legacy IHT205 route

Executors still see the old IHT205 form name online and in older probate discussions.

That can create confusion. The safest approach is not to assume an older form or publication still applies to the estate in front of you. Use the current GOV.UK route-checking guidance and make sure the date-of-death and estate type fit the route being used.

The evidence that matters

By the time you choose the reporting route, you should usually have or be chasing:

evidence for the date-of-death values
records of gifts and trust involvement where relevant
details of spouse, civil-partner, charity, or other exemption issues
notes showing why the estate is being treated as excepted or non-excepted
any documents supporting relief or nil-rate band claims

That record is what turns a form choice into a defensible tax position.

Common mistakes at this stage

Executors often create avoidable problems when they:

decide the form route before the asset picture is complete
ignore gifts, trusts, or foreign issues because they are inconvenient
assume the nil-rate band position is automatic without checking the conditions
keep the figures but not the evidence behind them
treat a form name as the whole tax analysis

The form is the output. The estate evidence is the real work.

Using Estate Suite for the tax-assessment stage

Estate Suite works best here when:

assets and liabilities already have supporting documents attached
gifts, trusts, and special claims are recorded explicitly
missing tax evidence is kept visible as an open task
the IHT section reflects the same figures used elsewhere in the estate record

That makes it much easier to move into [How to Pay Inheritance Tax Before Probate](/support/knowledge-base/how-to-pay-inheritance-tax-before-probate) and the probate application itself.

Good next reads

[How to Value Estate Assets and Debts for Probate](/support/knowledge-base/how-to-value-estate-assets-for-probate)
[IHT Gifts and Trusts Checklist](/support/knowledge-base/iht-gifts-and-trusts-checklist)
[Transferable and Residence Nil-Rate Band Claims](/support/knowledge-base/iht-transferable-and-residence-nil-rate-band-claims)