The amount actually paid to the Feds in 2020 is still the correct number.
But
You can add in any Fed estimate you made for 2019 in Jan of 2020
....and also any Federal balance due for 2019 (or any other year) that you actually paid during 2020.
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Most (or maybe all) of the few States that allow a Federal taxes paid income deduction, also work this way.
Certainly the instructions MT provides:
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Line 4 Federal Income Tax.............. Enter the total amount of federal income tax paid during 2020.
...and...
4b. Enter the amount of federal estimated income tax payments;
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...could leave some room for interpretation...but I don't think so.
You could always call the MT tax people and ask for clarification....there should be a number on their website.
____________*Answers are correct to the best of my knowledge when posted, but should not be considered to be legal or official tax advice.*
