(a) "Estimated tax" defined. For purposes of this Code section, the term "estimated tax" means the amount which the individual estimates as the amount of income tax imposed by Code Section 48-7-20 less the amount which the individual estimates as the sum of credits allowable by law against the tax.

(b) Requirement of estimated tax. Except as otherwise provided in subsection (d) of this Code section, every resident individual and every taxable nonresident individual shall file his estimated tax for the current taxable year if he can be reasonably expected to be required to file a Georgia income tax return for the current taxable year and his gross income can reasonably be expected to:

(1) Include more than $1,000.00 from sources other than wages as defined in paragraph (10) of Code Section 48-7-100; and

(2) Exceed:

(A) One thousand five hundred dollars if the individual is single or the individual is married and not living with his spouse or the individual is married and expects to claim only $1,500.00 of the marital exemption; or

(B) Three thousand dollars if the individual is married and living with his spouse and expects to claim the full marital exemption.

(c) Return as estimated tax. If on or before January 31 of the succeeding taxable year or, in the case of an individual referred to in subsection (b) of Code Section 48-7-115, relating to income from farming and fishing, on or before March 1 of the succeeding taxable year, the taxpayer files a return for the taxable year for which the estimated tax is required and pays in full the amount computed on the return as payable and the estimate is not required to be filed during the taxable year but is required to be filed on or before January 15, then the return shall be considered as the estimate.

(d) Exemptions. This Code section shall not apply to an individual in a given tax year if:

(1) The sum of the allowable credits shown on the individual's income tax return for the tax year exceeds the individual's tax liability shown on the return before the tax liability is reduced by the amount of the allowable credits; and

(2) The individual reasonably expected at the time estimated tax was otherwise required to be filed with respect to the tax year that the conditions of paragraph (1) of this subsection would be met for the tax year.

(e) Applicability to fiduciaries. With respect to taxable years beginning on or after January 1, 1988, fiduciaries shall be subject to all requirements of this article in the same manner as individuals.