Knowing that mistakes and omissions happen on corporate tax returns, the Internal Revenue Service provides Form 1120X to amend a previous filing. You might want to amend your corporation's return for one of several reasons, including changes in your filing status, omissions or to take advantage of changes in the tax law following the 2010 Small Business Jobs Act. Typically, you have up to three years from your original filing to amend a return. However, if your amended return causes you to owe more in taxes, the IRS will charge you interest on any unpaid amount. Consult with your tax professional before filing an amended corporate return.
Gather any documentation to substantiate the changes you are making on your amended return. If your amended return is due to a change in your deductions, credits or income, this information includes any forms, statements or schedules that validate the changes you are making.
Download Form 1120X from the IRS website. You also need Form 8886 if
you are amending a year in which your corporation had a reportable transaction from a tax shelter.
Make a copy of the tax computation page and Page 1 of Form 1120 from the year you are amending and the year the year you reported the credit or loss if you are amending your return to claim a carryback.
Complete the required forms. Eligible small business claiming a carryback of an eligible small business credit (ESBC) should enter "SBJA" and the current year on the top of your amended return. If you are reporting a carryback claim for a net operating loss, write "Copy Only -- Do Not Process" on the top of the attached schedules and forms.
Pay any tax due electronically through the IRS' tax payment system or include a check with your filing. Make your paper check out to the "United States Treasury."
Sign and date any forms necessary. Mail the amended return to the IRS Service Center that processed your original return.