Get your taxes done using TurboTax

You could do a fake test return in a new account to see what the difference would be by filing Joint.  You don't need to pay unless you want to print it.

 

Online is only good for 1 return per account.  But you can use the same email address for 5 accounts.   How to start another return in the Online version

https://ttlc.intuit.com/community/using-turbotax/help/how-do-i-start-another-return-in-turbotax-onli...

 

Or do a new return in the Desktop program.