Estimated Income Tax Corporations that expect to have an income tax liability to this State of $500 or more are required to file Form CD-429, Corporate Estimated Income Tax, and pay estimated income tax. The term "estimated tax" means the amount of income tax the corporation expects to owe for the taxable year after subtracting any tax credits. The term "taxable year," for the purpose of filing declarations of estimated tax, means the calendar or fiscal year in which the company expects to earn the income upon which the estimated tax is based. Form CD-429, Corporate Estimated Income Tax, is used to pay corporate estimated income tax. Payments of tax are due to be filed on or before the 15th day of the 4th, 6th, 9th and 12th months of the taxable year. Failure to pay the required amount of estimated income tax will subject the corporation to interest on the underpayment. (Use Form CD-429B to calculate the interest.) You can pay corporate estimated income tax payments online. Go to "eServices" and select "CD-429".