The most important thing to know about a Tax Extension is that an extension to file your taxes is not an extension to pay your taxes. Sole Props, Single Member LLCs, and C-Corps will need to remit their tax liability payments at the time of filing an extension. Partnerships and S-Corps will not owe a tax liability on March 16. As these entities pass the tax liability on to the individual, the payment of that tax liability is due at the time the personal return is filed - April 15, 2021.