Do I have to file an amendment if I found a mistake which doesn't change my taxes due, only the capital loss carryover amount?

[Mike414]

I found an error in the previous year's return. The correction will change my capital gains, but it will not change the tax due, since I had a capital loss carryover which offset my capital gains in full. According to the correction, I will have a larger capital gain, which would be still offset by the capital loss carryover, however the carryover will be lower now. (So this would materially impact my taxes sometime in the future).

Do I have to file an amended return in this case? Or is there another way to correct my capital loss carryover without an amended return?

[WillK]

Yes, you should amend your return since you noticed there is an error on the original return. . If you already filed your return you will need to wait to see if it was rejected or accepted. If they were rejected you are able to login to your return to fix what you need to fix and fix the errors that caused the rejection and refile the return. If your returns were accepted, then you will need to file an amended return. You should not try to amend your return until the original return it has been fully processed and you have received your refund or your payment has cleared.

Amended returns do not “catch up” to your original return and replace them; they are processed as two separate returns.  
Amended returns have to be printed and filed by mail.  It can take the IRS up to 12 weeks or longer to process them.   If you are due a larger refund than on your original return, your amended return should only show the difference and you will receive a separate check for it.  If you owe money on your amended return, it will show only the new amount owed, you will have to mail a check with the return. You can check the status of your amended return by clicking here: https://www.irs.gov/filing/individuals/amended-returns-form-1040-x-/wheres-my-amended-return-1

 Click here for amending instructions: https://ttlc.intuit.com/replies/3288565

[Mike414]

Thanks for the detailed response!
One more question: how do I correct the capital loss carryover in my current (2016) return?
I found the error in my 2015 return, which I will amend by sending in a 1040X on paper. According to the amended return, my capital loss carryover for 2016 will be reduced. However, I started on my 2016 taxes already, using the original 2015 return, and as a result, the carryover amount is incorrect now in my 2016 return (I haven't filed it yet). How do I fix the carryover amount, so that it reflects the correct, amended amount?