Need help. I amended my 2021 return cause I omitted income (12K) that was inadvertently missed on a 1099R form. Do I just mail in the 1040x form? Everything I read says to mail in all forms that changed but how do I know if any forms in my 1040 changed? Or do I just submit the 2 pages of the 1040x with my check?
Amending because of a Form 1099-R you only need to mail in the Form 1040-X and a copy of the Form 1099-R along with your check if you have taxes owed.
It's not necessarily so simple. For example, the 1099-R increases your income. The additional income could change a deduction or credit on another form. As another example, if the 1099-R that you added is an early withdrawal from an IRA, you would need Form 5329. These are just a couple of examples. There are other situations where a form could be added or changed.
I don't have a simple answer for you. You should compare the entire amended return to the original return to see what forms have changed or been added.