(a) "Estimated tax" defined. For purposes of this Code section, the term "estimated tax" means the amount which the corporation estimates as the amount of income tax imposed by Code Section 48-7-21 less the amount which the corporation estimates as the sum of credits allowable by law against the tax.

(b) In general. Every domestic and foreign corporation subject to taxation under Code Section 48-7-21 shall pay estimated tax for the taxable year if its net income for the taxable year as defined in Code Section 48-7-31 can reasonably be expected to exceed $25,000.00.