There is a lot of misinformation in this thread, (e.g. references to form 1040 lines that don't exist, like "line 70"), and I too wasted hours trying to figure out how to get Turbotax to include the payments with Federal extension on Form 1040, and to then properly calculate the total federal tax owed or to be returned when filing, and finally succeeded.
The key is not to enter it into the "easy steps" using the additional payments area of Deductions, but rather to open up Schedule 3, go to the area for additional payments with extension, click on the field for the payment amount enter the payment into the dialog box that appears.
