(a) General Rule. If the estimated tax required to be paid by Section 19025 for a taxable year is in excess of the tax due for that taxable year, any overpayment shall be credited or refunded as provided in Section 19301 to 19364, and the regulations issued thereunder.

(b) Date of Overpayment. There can be no refund of the estimated tax until the entire tax liability has been satisfied. Any amount paid as estimated tax for any taxable year shall be deemed to have been paid on the last day prescribed for filing the return (determined without regard to any extension of time for filing such return.)

(c) Period for Which Interest Allowable in Case of Refunds. If an overpayment of an estimated tax is refunded, interest shall be allowed from the date of the overpayment to a date determined by the Franchise Tax Board, which shall be not more than 30 days prior to the date of the refund check. The acceptance of a refund check shall not deprive the taxpayer of the right to make a claim for any additional overpayment and interest thereon, provided the claim is made within the applicable period of limitation. However, if a taxpayer does not accept a refund check, no additional interest on the amount of the overpayment included in such check shall be allowed.

(d) Period for Which Interest Allowable in Case of Credits.

If an overpayment of estimated tax is credited, interest shall be allowed from the date of the overpayment to the date of the allowance of the credit as provided by Section 19340.