Is basis of house at date of death or date of transfer?

[9corners]

Father passed away last year in May.

Irrevocable trust instructed to distribute to my siblings and I.

Transferred grant deed ownership of house last year in December.

Is basis of house for siblings at the date of transfer in December, or at date of death in May?

[Anonymous_]

You mentioned "irrevocable" with respect to the trust so it could be either a carryover basis or a stepped-up basis; more details concerning the trust are needed.

To put it simply (and admittedly incomprehensibly to the uninitiated), if the principal (corpus) of the trust was included in your father's gross estate, the property so included will receive a stepped-up basis.