If you just want to compare how filing separately would work out, since you are using the CD/Download desktop TurboTax software you can use the What-If Worksheet in forms mode.
First complete your joint return. Then go to forms mode and open the What-If Worksheet. After you open the form, before you do anything, click on Help Center. In the introductory information at the top of the Help, scroll down a bit until you see the following paragraph.
"If you are preparing a Married Filing Joint vs Married Filing Separate comparison, it is very important that you read preparing a Married Filing Joint Versus Married Filing Separate Analysis."
The underlined part of that sentence is a link. Click on that link in the Help (not here in the forum) and follow the instructions there.
