April 15 - Normal due date for income tax returns and to request an extension of time to file your return. Any tax you owe should be paid with the extension.
October 15 - Last day to file a return under automatic extension.
January 15 - 4th installment payment for previous year
April 15 - 1st installment payment
June 15 - 2nd installment payment
September 15 - 3rd installment payment