Print and mail the 2017 Form 4868 Application for Automatic Extension of Time
To File U.S. Individual Income Tax Return. Mail to the IRS after January 1, 2018.
Go to this IRS website for Form 4868 - https://www.irs.gov/pub/irs-pdf/f4868.pdf
Note that filing an extension request only gives you an extra six months to file a federal tax return. It is not an extension for payment of any federal income taxes owed, which are due to paid on or before April 17, 2018.
