I need to make estimated payments by Jan 15 but the mortgage interest expense section will not let me input anything until Jan 17 or later?

[Critter]

For the benefits of estimating ONLY ( and you will need to undo this when you file for real) you could enter the mortgage interest as a donation ... this will have the same effect for now.

[Texas Roger]

OR you can manually add up all your itemized deductions and see if they exceed the standard deduction for your filing status. If they don't exceed the standard deduction, then you can't use your itemized deductions. You can look at a draft Schedule A to see what is included in itemized deductions: <a rel="nofollow" target="_blank" href="https://www.irs.gov/pub/irs-pdf/f1040sa.pdf">https://www.irs.gov/pub/irs-pdf/f1040sa.pdf</a>

Note that you can only deduct the amount of medical expenses that exceed 7.5% of your Adjusted Gross Income and the Taxes Paid deductions are limited to $10,000.

[DoninGA]

Schedule A will not be finalized until 01/17/2019.  The IRS has not yet finalized the instructions for Schedule A.  Until the IRS finalizes the federal forms, schedules, instructions and calculations, TurboTax cannot finalize the forms and schedules included in the software. 

The IRS has not yet even published a date when they will be accepting any type of 2018 tax return.  It is estimated to be sometime in either late January or early February.  

With all the tax code changes and changes to the tax forms it would be wise to wait until mid to late February or even early March before anyone should file their 2018 tax return to make sure that most if not all the bugs have been fixed in the IRS systems due to the changes.