What is Basic Obligation in Terms of Subnitting IHT Return

[Claudius]

My mother has a half share in her property and is now very frail.
I need to know whether the higher IHT allowance for immediate offspring inheritances needs to be formally claimed on death via a IHT return.
If not, if I calculate that at death, her estate, incl above allowance is less than the nil rate figure, are we exempt from having to submit a return?
Thank you.

[pawncob]

https://www.gov.uk/hmrc-internal-manuals/inheritance-tax-manual/ihtm06012

[maths]

Check if the estate qualifies as an excepted estate (see below; to do this the residence nil rate band is not taken into account):

https://www.gov.uk/hmrc-internal-manuals/inheritance-tax-manual/ihtm06011

If the RNRB is to be claimed then IHT 400 needs to be completed.