After you file

Yes you can use the 2018 Desktop program to estimate in a couple ways.

 

You can go though the Estimated Tax section which will prepare estimated payments for next year.  That may help you calculate what you might owe.  You can just type W4 in the search box at the top of your return , click on Find. Then Click on Jump To and it will take you to the estimated tax payments section. Say no to changing your W-4 and the next screen will start the estimated taxes section.

 

OR go to

Federal Taxes or Personal (H&B version)

Other Tax Situations

Other Tax Forms

Form W-4 and Estimated Taxes - Click the Start or Update button

 

In the Desktop Software there is also a What-if worksheet. Go to Forms Mode, click Forms in the upper right (left for Mac). Then click Open Forms box in the top of the column on the left. Open the US listing of forms and towards the bottom find the What-if worksheet.  Or you can copy your file with another name and test in the copy.  Go to FILE-SAVE AS.

 

But you can't pay the estimated payments from Turbo Tax.  You can pay directly on the IRS website https://www.irs.gov/payments

Be sure to pick the right kind of payment and year.....2019 Estimate