Autofill Act of 2013 - Amends the Internal Revenue Code to require the Secretary of the Treasury to: (1) establish a program to allow taxpayers to download income tax forms that are populated with tax return information (e.g., wages, withholding, and self-employment income) previously reported to the Secretary for the taxable year; (2) establish standards for data download to tax preparation software; and (3) provide on the website of the Department of the Treasury a secure function that allows a taxpayer to download, as both a printable document file and in a form suitable for input to automatic tax preparation software, the 1040, 1040A, and 1040EZ forms that are populated with tax return information previously reported to the Secretary. Establishes deadlines for reporting tax return information to the Secretary and for making such information available for populating tax returns.