To avoid, or at least mimimize any penalties and interest from the IRS, you do still have to pay your taxes by the April deadline. If you are unsure of the amount or don’t think you can pay it all, tax experts advise that you pay what you can afford, or what you think you might owe, and then apply for an extension for filing your taxes. This will reduce any interest or penalties until you file. If you overpay, once you do file it will just come back to you in your refund.
If you can’t afford to pay all of your taxes, the IRS web site (irs.gov) will help you see if you are eligible for an Installment Agreement. If so, you can apply using the Web-based Online Payment Agreement application.
To obtain an extension, just use Form 4868, Application for Automatic Extension of Time to File U.S. Individual Income Tax Return. The form is available at the IRS web site, http://www.irs.gov. On the site just do a search for Form 4868.