If you can't meet the mid-April deadline to file your tax return, you can get an automatic six-month extension of time to file your return from the IRS. The extension will give you extra time to get the paperwork in to the IRS, but it does not extend the time you have to pay any tax due. You will owe interest on any amounts not paid by the mid-April deadline, plus a late payment penalty if you have paid less than 90 percent of your total tax by that date. All amounts that you enter on your Form 4868 should be the amounts that you expect to report on your return. They do not have to be the exact calculations, but they should be relatively accurate estimates.