Can I amend my 2018 Tax return? I found something was wrong? I have not mailed it yet.

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If you plan to mail in your return, you can go back and make the adjustment and print and mail the adjusted copy.

If you plan to e-mail your return.

If the return has not been submitted, you can go back and correct it.

If your return has been submitted, you should wait to determine if it has been rejected or accepted.

If rejected, you can go back and change or adjust your return. .

Once accepted by the IRS, you should wait until you receive your refund or paid your balance due to amend the return.

When you amend, if the result does not make a difference, you can disregard it.

If the result does change, print and mail the amendment a (it cannot be e-filed) and allow about 16 weeks for processing.

 See Do I Need To Amend My Return?

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In other words, you won't file an amendment until your return has been accepted by the IRS, and you have received your refund or paid your tax due. Up until acceptance, you may be able to correct your original return.