You can choose whether to file for your IRS Form 4868 extension online or through the mail. If you file online, you can use 1040.com, an official provider of IRS e-file services for 1040 returns and 4868 extensions.
If you choose to file through the mail, fill out Form 4868 and send to the address shown on page 4 of the form.
Remember: Extension applications are due by April 15 (or the next business day, if the 15th falls on a holiday or weekend), and any taxes you owe are also due on that date. With an extension, your return will be due October 15 (or the next business day, if the 15th falls on a holiday or weekend). For those in military or living outside the U.S, special rules may apply.