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It depends. Don't amend if:

• Your e-filed return is rejected. Just make your changes before you resubmit or mail your return.
• Your e-filed return is still pending. Wait until the return is accepted before amending. If rejected, make your changes before you resubmit or mail your return.
• You received a government notice that doesn't specifically tell you to amend (e.g. math error corrections, request for additional forms, etc.). Follow the instructions in the notification.
• You received Forms 1095-B or 1095-C and the info matches what you reported on your return. 

On the other hand, you will need to amend if you already mailed your return (or the government accepted your e-file) and:

• You need to report a tax form you forgot about or received post-filing (most commonly a W-2, 1099, or 1095-A).
• You received a corrected tax form after filing (the "corrected" box is checked) and the new info changes your refund or tax due amount.
• You forgot to report income or claim dependents, deductions, or credits.
• You accidentally claimed dependents, deductions, or credits you're not eligible for.
• You made an error that affects your bottom line, such as reporting income or deductions in 2016 that should've been claimed in a prior tax year (in that case, you'll need to amend all affected tax years).
• You need to change your filing status (e.g., you want to change from Single to Head of Household).
• We instructed you to amend because of a program error (uncommon).