The 1040X is difficult to understand since it is not set up to mirror a 1040.
If you have an overpayment in the original year, and apply it to the next tax year, that applied over-payment will not change. It is reported on line 18 of the 1040X. It is not an amount that can be adjusted.
For example, if your tax liability in 2017 is $210 and you paid in $300, you will get a $90 refund. You can choose to apply that 90 to 2018.
You amend your 2017 return and now your tax liability is $300. You paid 300 AND applied 90, so you will actually owe 90 with the amended return and you will get a 90 credit on your 2018 tax return.
It might make more sense if you understand that very often an amended return is calculated years after the original. If there was an overpayment applied, it would be impossible to change it since it had already been applied. If I filed in 2015, applied an overpayment to 2016, then amended my 2015 return in 2018, the overpayment has already happened.
On an amended return, the IRS treats all overpayments applied to next year as having already happened.
[edited 01-17-19I6:29pm]
I received a (significantly) amended K-1, which changes passive loss carryover amounts.
I see, if you are only changing the carry-over, line 23 should be the same as the original.
The 1040X is difficult to understand since it is not set up to mirror a 1040.
If you have an overpayment in the original year, and apply it to the next tax year, that applied over-payment will not change. It is reported on line 18 of the 1040X. It is not an amount that can be adjusted.
For example, if your tax liability in 2017 is $210 and you paid in $300, you will get a $90 refund. You can choose to apply that 90 to 2018.
You amend your 2017 return and now your tax liability is $300. You paid 300 AND applied 90, so you will actually owe 90 with the amended return and you will get a 90 credit on your 2018 tax return.
It might make more sense if you understand that very often an amended return is calculated years after the original. If there was an overpayment applied, it would be impossible to change it since it had already been applied. If I filed in 2015, applied an overpayment to 2016, then amended my 2015 return in 2018, the overpayment has already happened.
On an amended return, the IRS treats all overpayments applied to next year as having already happened.
[edited 01-17-19I6:29pm]
Yes, agreed, but TurboTax is showing 0 on Fm 1040X Ln 23 and there doesn't seem to be any way to change it. Can I somehow open Fm 1040X and amend it?
To clarify: Ln 23 on Fm 1040X = 0, but Ln 77 on the "new" Fm 1040 still shows the original amount applied to 2018 tax.
Yes, you can edit that....did you use your TurboTax 2017 to compute the 1040X?
Line 18 on the 1040X has you account for the overpayment you had on your original return.
It should still show on your 2018 return. For example, if you paid 1000 in tax, and had 250 applied to 2018, that 250 should still show on 2018 because the amended return has you subtract it from tax paid on line 18 of the 1040X
Please see the updated answer, an overpayment applied to next year does not change.
In conclusion, if I'm understanding you correctly, Ln 23 of the 1040X indicates the additional amount (if any) that should be applied (credited) to my account at the time of filing of the 1040X return. The amount shown on Ln 77 of the original 1040 return has already been applied and will not change. In my case, since the tax amount remains the same, Ln 23 of the 1040X should, in fact, be zero.