Tax Return Due Date Simplification and Modernization Act of 2011

Tax Return Due Date Simplification and Modernization Act of 2011 - Amends the Internal Revenue Code to change tax return due dates for partnerships (from April 15 to March 15, with extensions until September 15), S corporations (from March 15 to March 31, with extensions until September 30), and C corporations (from March 15 to April 15, with extensions until October 15). Makes the new return date for C corporations with a fiscal year ending on June 30 applicable to taxable years beginning after December 31, 2021.

Requires the Secretary of the Treasury, for taxable years beginning after December 31, 2011, to modify by regulation the due dates for extensions of tax returns for partnerships, estates, employee benefit plans, and tax-exempt organizations. Sets a due date of April 15 for the annual information return of a foreign trust with a U.S. owner and for the report of foreign bank and financial accounts (with extensions until October 15).

Extends the automatic extension for corporate income tax returns from three to six months (seven months for C corporations with a fiscal year ending on June 30).