Since it is not a small change (missing form or math miscalculation), missed income probably requires that you file an amendment. You’ll need to file Form 1040X, Amended U.S. Individual Income Tax Return. Additionally, if any changes you are making need forms or schedules attached, make sure you do so.
Don’t panic, you have three years since the date of filing or two years from paying (whichever is later) to correct the issue. But note, if your amended return claims more refund money, go ahead and cash your original refund check – no need to wait the average 12 weeks it takes to process your amended return. However, if your amended return shows you owe, you’ll want to lower fees and interest by paying those taxes as fast as you can.
You can then track the status of your amended tax return(s) with the IRS’s ‘Where’s My Amended Return’ tool. Check the IRS’s site about three weeks after you’ve mailed your amended return or call 866-464-2050.