It is quite likely that Mitt and Ann have investments in small corporations or partnerships where the company earnings flow directly to the shareholders/partners. If the small corporation or partnership got an extension of time to file the federal tax return, then Mitt and Ann can't file because they don't have all the information (Schedule K-1) they need to file. Lots of investors extend their tax returns through no fault of their own - simply waiting on someone else to finish up needed paperwork. Oh, BTW, getting an extension to file doesn't mean you get an extension to pay your taxes. If you don't pay any amount you expect to owe with your extension, then the IRS assesses a late filing penalty. Just FYI.