You have up to three years to make changes -- and claim any deductions or credits you might have missed. By Kimberly Lankford, Contributing Editor March 19, 2012 I just realized that I qualified for a tax credit in 2010 but didn’t claim it on my return that year. Is it too late to get the money?You have up to three years after the due date of your return to file an amended return using Form 1040X. It isn’t necessary to refile your whole return -- just note the changes you’re making and include revised copies of any supplemental forms that are affected (such as Schedule A for changes to itemized deductions, or Form 8863 for the American Opportunity Credit). If the change lowers your tax bill, the IRS will send you a refund. See the Instructions for Form 1040X and the IRS’s amended return page for more information. Reducing your federal income tax could also lower your state income tax liability. File your amended federal return first, then get a copy of the transcript of your account from the IRS (confirming that you amended your federal return) and file an amended return with your state, with a copy of your Form 1040X. Before you file your amended return, go through our list of Most-Overlooked Tax Deductions to see if you’ve missed any other tax breaks. Got a question? Ask Kim at firstname.lastname@example.org.