If you need to amend your federal tax return, you'll use IRS Form 1040X, which is especially designed for that purpose. The 1040X instructions provide detailed information about what to submit with your return, though exactly what you need to include depends on what you're amending and what you initially filed.
You generally must submit any tax forms and paperwork you need to support the changes you're making to your return as 1040X attachments, so you may need to submit new tax forms for new income or deductions and may be able to leave out some forms you included with your original tax return. You should not include a copy of your original return with your amended return.
How to File a 1040X Amended Return
If you realize you've made a mistake or had incomplete information on your tax return, you can file a 1040X amended return with the Internal Revenue Service to update your return. The amended return must be filed on paper by postal mail, though you can pay any additional tax owed electronically. If you're filing amended returns for multiple years, mail them separately.
Once you file an amended return, it will usually take eight to 12 weeks, or in some cases as many as 16 weeks, to be processed by the IRS. You can track the return's status online starting about three weeks after you file it.
Follow the 1040X instructions to update any information that needs to be amended in your return. Update any personal information that needs to be updated and indicate what values from your original return need to be updated, what they're being changed to and what the net difference is. Write a brief explanation of why you're amending your return in Part III of the 1040X.
You should attach any documents that support the reasons for your change. This can include tax forms such as W-2s or 1099-MISC forms from which you copied incorrect information on your previous return or entirely new forms that you've received since you filed or erroneously didn't include, such as if you didn't include a W-2 from an employer.
Also attach any schedules that support your changes. For example, if you are claiming new itemized deductions, you would attach an amended Schedule A, and if you were claiming new business income or expenses, you would attach an amended Schedule C.
Generally don't include unnecessary paperwork with the amended return.
When You Can't or Shouldn't File
Note that you generally must file an amended return within three years of filing your initial return, or within two years of paying any tax due, whichever date comes later.
If you are being audited by the IRS or the IRS changes your return based on its own information, you generally don't need to file an amended return. If an IRS audit finds that your return was incorrect, you can either agree to its changes and pay any tax owed or receive any refund due or contest them. Either way, you don't need to use Form 1040X to respond to an audit.
Tax Law Changes for 2018
While the amended return process isn't changing in 2018, many sections of tax law are. Remember that 2018 brings new standard deductions, tax brackets and tables and permissible itemized deductions. Make sure that you're using the current forms and instructions, or you may need to amend your return.
Amending Returns from 2017 and Previous Years
If you're amending a previous year's return, always use the instructions and tax laws from that year, not the current year. Tax law changes going into effect in 2018 do not affect previous year's initial or amended tax returns, even if you're filing them in 2018 or later.