If you are using download TurboTax (TT), there is a What-If worksheet that can provide that info. It's not available with Online TT.
Using the TurboTax desktop editions, click on Forms. When in Forms mode click on Open Form at the to left of the Forms mode screen. Type in what-if. Click on the result to open the What-If Worksheet.
At the top of the work sheet, click on MFJ vs MFS.
The What-If Worksheet does not affect your actual tax return.
