If you have come to the realization that you forgot to include an item of income, deduction, credit, etc. from the tax return that you have already filed, you may still have time to make a correction by amending your tax return. 

Generally speaking, you have three years to correct (or “amend”) your Form 1040, by filing Form 1040X.  If you also file a state tax return, you may (or may not) also have to file an amended return as well.

According to the IRS, you can fix mistakes or omissions on your tax return by filing an amended tax return. If you need to file one, these tips can help.

1. Must be filed on paper.Use Form 1040X, Amended U.S. Individual Income Tax Return, to correct your tax return. It can’t be e-filed. You can get the form on gov/forms at any time. See the Form 1040X instructions for the address where you should mail your form.
2. Amend to correct errors.File an amended tax return to correct errors or make changes to your original tax return. For example, you should amend to change your filing status, or to correct your income, deductions or credits.
3. Don’t amend for math errors, missing forms. You normally don’t need to file an amended return to correct math errors on your original return. The IRS will automatically correct those for you. Also, do not file an amended return if you forgot to attach tax forms, such as a Form W-2 or a schedule. The IRS will mail you a request for them in most cases.
4. Form 1095-A, Health Insurance Marketplace Statement, errors.Some taxpayers may receive a second Form 1095-A because the information on their initial form was incorrect or incomplete. If you filed a 2015 tax return based on the initial Form 1095-A and claimed the premium tax credit using incorrect information from either the federally-facilitated or a state-based Health Insurance Marketplace, you should determine the effect the changes to your form might have on your return. Comparing the two Forms 1095-A can help you assess whether you should file an amended tax return, Form 1040X. 
5. Three-year time limit.You usually have three years from the date you filed your original tax return to file Form 1040X to claim a refund. You can file it within two years from the date you paid the tax, if that date is later. That means the last day for most people to file a 2012 claim for a refund is April 18, 2016 (April 19 for taxpayers in Maine and Massachusetts). See the Form 1040X instructions for special rules that apply to some claims.
6. Separate forms for each year.If you are amending more than one tax return, prepare a 1040X for each year. You should mail each year in separate envelopes. Note the tax year of the return you are amending at the top of Form 1040X. Check the form’s instructions for where to mail your return.
7. Attach other forms with changes.If you use other IRS forms or schedules to make changes, make sure to attach them to your Form 1040X.
8. When to file for corrected refund.If you are due a refund from your original return, wait to get it before filing Form 1040X to claim an additional refund. Amended returns take up to 16 weeks to process.
9. Pay additional tax.If you owe more tax, file your Form 1040X and pay the tax as soon as you can to avoid possible penalties and interest from being added to your account. Use IRS Direct Pay to pay your tax directly from your checking or savings account.
10. Track your amended return.You can track the status of your amended tax return three weeks after you file with ‘Where’s My Amended Return?’ It is available in English, Spanish, Chinese, Vietnamese and Russian. The tool can track the status of an amended return for the current year and up to three years back. If you have filed amended returns for multiple years, you can check each year, one at a time
    
    Source: https://www.irs.gov/uac/Amending-Your-Tax-Return-Ten-Tips
    
    

Do you have a question about filing an amended return or other income tax concerns? We are ready to start the conversation. Contact at info@zinnerco.com or 216.831.0733 for a no-cost, no-obligation consultation.