Every U.S. corporation that is taxed as a corporation is required to file its income tax return on or before April 15 in every year or October 15 if they have filed an extension. The extension is an extension to file the income tax return, not to pay a liability for tax.
For U.S. corporations who have made a S Corporation election the income tax return due date is March 15 and the extended due date is September 15.
U.S. Corporations are subject to federal taxation at the flat rate of 21% on U.S. profits. Those profits will also be subject to state taxation if they are sourced in a particular U.S. state.
Dividends paid by a U.S. Corporation to U.S. resident taxpayers will be liable for tax of 20% of qualified dividends and at ordinary income tax rates on dividends that are not qualified dividends. Dividends paid to residents will also be subject to Net Investment Income Tax of 3.8%.
Dividends paid by a U.S. Corporation to a non resident taxpayer will be subject to withholding tax at the rate of 30% if the shareholder is living in a non treaty country and a reduced rate of 5% to 15% if they are living in a treaty country.