Cal. Code Regs. tit. 18 § 13983
If paid by the decedent's estate or the transferee of the property, the unpaid amount of any bona fide, allowable, and legally enforceable unsecured debt of a decedent existing at the time of his death, together with any interest thereon which had accrued at the time of death, may be deducted from the market value of property transferred by the decedent.
Any tax which is not deductible under Revenue and Taxation Code Section 13987, relating to state, county, and municipal taxes which are a lien against property included in any transfer subject to the Inheritance Tax Law, but which was a personal obligation of the decedent at the date of his death and is paid by the decedent's estate may be deducted as a debt of the decedent under Revenue and Taxation Code Section 13983.
NOTE: Reference: Section 13983, Revenue and Taxation Code.
Cal. Code Regs. Tit. 18, § 13983