Investors & landlords

When working with federal or state returns (assuming you've already filed them), if you make an error, you must file an amended return. Most states show the standard tax form no. with an X suffix (e.g., you would use Form 1040X to amend a 1040 return). Also, most states do not allow you to e-file an amended return; you must snail-mail the paperwork to your state revenue office.