If you’re e-filing your return and the system rejects it
If you’re using IRS’s fillable forms, and the E-file system rejects your return, it’ll provide an error code, telling you where the problem is. Some rejected returns are caused by incorrectly entering a Social Security number or other taxpayer identification number. Usually you can correct the error and try to file again. IRS.gov has a tool to walk you through common rejections. If you make the correction and the system still rejects the return, you can send it by mail. (For more information about e-Filing, see Free File.)
If you made a mistake and realize after the due date for filing, but before the IRS discovers the mistake
In this case, you can generally file an amended return, but you must mail it to the IRS.
If there is a mistake and the IRS sent you a notice or returned the form
If information is missing, the IRS will either return the form or send a notice asking you for specific information it needs to finish processing your return. Simply send the information to the address on the notice or call the number on the notice if you have questions.
If the IRS changed an amount on the return
The IRS sometimes makes changes because of a miscalculation. The IRS might also believe, based on other information on the return, that you’re eligible for a credit you didn’t claim.
No matter the reason for the change, if you disagree at all, reply immediately.
Gather any documentation to support your position and be ready to fax it.
Contact the IRS by mail or by calling the number on the notice you receive.
Follow the IRS’s instructions to submit any supporting documentation and always keep copies.
The IRS is considering changing an amount on the return, due to an examination after the return has been processed.
This is called an audit. If it audits your return, the IRS will notify you by mail, and the notice will tell you if the audit will be handled by mail or in person. For more information, see Audits by Mail or Audits in Person.
If you receive a different refund amount than you expected or none at all
Changes to returns during processing and other situations can affect the size of your refund.
Where is My Refund has information on locating and claiming a refund.