Get your taxes done using TurboTax

By the way what state are you in?  If you are  in a Community Property state MFS gets tricky to figure out.  

Find the What-If worksheet.
Go to Forms Mode, click Forms in the upper right or on the 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. It's right under Estimated Taxes.

Or try…Go into Forms View. Once there, at the top of the left column, click on the icon for "Open Form". A popup window will appear. In the text line, type the word "what" without quotes. You should see "what-if worksheet" appear as a selection choice. Double-click it to launch the form.