Due to COVID the IRS is actively (though temporarily) changing deadlines for these next couple months. The extended deadline is October 15, 2021. If the corporation operates on a fiscal year, the deadline is the 15th day of the fourth month following the end of the corporation’s fiscal year. Texas, Oklahoma, and Louisiana Because of the storms that hit these states, the deadline for taxes normally due on March 15th and April 15th has been extended. The IRS announced on February 22nd that these states have until June 15th, 2021 to file and pay business returns.