(a) For purposes of this part, “deficiency” means the amount by which the tax imposed by Part 10 (commencing with Section 17001) or Part 11 (commencing with Section 23001) exceeds the excess of—

1. (1) The sum of—

   1. (A) The amount shown as the tax by the taxpayer on an original or amended return, if an original or amended return was filed, plus
   2. (B) The amounts previously assessed (or collected without assessment) as a deficiency, over—
2. (2) The amount of rebates, as defined in paragraph (2) of subdivision (b), made.

(b) For purposes of this section:

1. (1) The tax imposed by Part 10 (commencing with Section 17001) and Part 11 (commencing with Section 23001) and the tax shown on an original or amended return shall both be determined without regard to payments on account of estimated tax, and without regard to the credit under Section 19002.
2. (2) “Rebate” means so much of an abatement, credit, refund, or other repayment, as was made on the ground that the tax imposed by Part 10 (commencing with Section 17001) or Part 11 (commencing with Section 23001) was less than the excess of the amount specified in paragraph (1) of subdivision (a) over the rebates previously made.