California Code, Revenue and Taxation Code - RTC § 19110

(a) When the correction of an erroneous inclusion or deduction of an item or items in the computation of income of a trust, estate, parent, or spouse for any year results in an overpayment for that year by the trust, estate, parent, or spouse, and also results in a deficiency for the same year for a grantor of the trust or beneficiary of the estate or trust, or child of the parent, or spouse of the child, or the spouse of the spouse, the overpayment, if the period within which credit for the overpayment may be allowed has not expired, shall be credited on the deficiency, if the period within which the deficiency may be proposed has not expired, and the balance, if any, shall be credited or refunded. No interest shall be assessed on the portion of the deficiency as is extinguished by the credit for the period of time subsequent to the date the overpayment was made.

(b) When the correction of an erroneous inclusion or deduction of an item or items in the computation of income of a grantor of a trust, beneficiary of an estate or trust, a child, or spouse of the child, or a spouse for any year results in an overpayment for that year by the grantor, beneficiary, child, or spouse, and also results in a deficiency for the same year for the grantor's or beneficiary's trust, the beneficiary's estate, the child's parent, or spouse of the child, or the beneficiary's spouse, the overpayment, if the period within which credit for the overpayment may be allowed has not expired, shall be credited on the deficiency, if the period within which the deficiency may be proposed has not expired, and the balance, if any, shall be credited or refunded. No interest shall be assessed on the portion of the deficiency as is extinguished by the credit for the period of time subsequent to the date the overpayment was made.

(c) Subdivisions (a) and (b) are not intended, nor shall they be construed as a limitation on the Franchise Tax Board's right to offset or recoup barred assessments against overpayments.