(a) The rate established under this section (referred to in other code sections as “the adjusted annual rate”) shall be determined in accordance with Section 6621 of the Internal Revenue Code, except that:

(1) (A) For taxpayers other than corporations, the overpayment rate specified in Section 6621(a)(1) of the Internal Revenue Code shall be modified to be equal to the underpayment rate determined under Section 6621(a)(2) of the Internal Revenue Code.

(B) In the case of any corporation, for purposes of determining interest on overpayments for periods beginning before July 1, 2002, the overpayment rate specified in Section 6621(a)(1) of the Internal Revenue Code shall be modified to be equal to the underpayment rate determined under Section 6621(a)(2) of the Internal Revenue Code.

(C) In the case of any corporation, for purposes of determining interest on overpayments for periods beginning on or after July 1, 2002, the overpayment rate specified in Section 6621(a)(1) of the Internal Revenue Code shall be modified to be the lesser of 5 percent or the bond equivalent rate of 13-week United States Treasury bills, determined as follows:

(i) The bond equivalent rate of 13-week United States Treasury bills established at the first auction held during the month of January shall be utilized in determining the appropriate rate for the following July 1 to December 31, inclusive. Any such rate shall be rounded to the nearest full percent (or, if a multiple of one-half of 1 percent, that rate shall be increased to the next highest full percent).

(ii) The bond equivalent rate of 13-week United States Treasury bills established at the first auction held during the month of July shall be utilized in determining the appropriate rate for the following January 1 to June 30, inclusive. Any such rate shall be rounded to the nearest full percent (or, if a multiple of one-half of 1 percent, that rate shall be increased to the next highest full percent).

(2) The determination specified in Section 6621(b) of the Internal Revenue Code shall be modified to be determined semiannually as follows:

(A) The rate for January shall apply during the following July through December, and

(B) The rate for July shall apply during the following January through June.

(b) (1) For purposes of this part, Part 10 (commencing with Section 17001), Part 11 (commencing with Section 23001), Part 32 (commencing with Section 61000), Title 25 (commencing with Section 100800) of the Government Code, and any other provision of law referencing this method of computation, in computing the amount of any interest required to be paid by the state or by the taxpayer, or any other amount determined by reference to that amount of interest, that interest and that amount shall be compounded daily.

(2) Paragraph (1) shall not apply for purposes of computing the amount of any addition to tax under Section 19136 or 19142.

(c) Section 6621(c) of the Internal Revenue Code, relating to increase in underpayment rate for large corporate underpayments, is modified as follows:

(1) The applicable date shall be the 30th day after the earlier of either of the following:

(A) The date on which the proposed deficiency assessment is issued.

(B) The date on which the notice and demand is sent.

(2) This subdivision shall apply for purposes of determining interest for periods after December 31, 1991.

(3) Section 6621(c)(2)(B)(iii) of the Internal Revenue Code shall apply for purposes of determining interest for periods after December 31, 1998.

(d) Section 6621(d) of the Internal Revenue Code, relating to the elimination of interest on overlapping periods of tax overpayments and underpayments, shall not apply.

(Amended by Stats. 2019, Ch. 38, Sec. 39. (SB 78) Effective June 27, 2019.)