To compare Joint to MFS. If you are using the Online version, do NOT change anything on your return. You would have to start with a new account and do a test return. You don't have to pay unless you want to print it out. So you might need 3 accounts, one for Joint and two MFS, one for each spouse.
How to Compare Joint to Married Filing Separately
https://ttlc.intuit.com/questions/2895312-how-can-we-compare-married-filing-jointly-with-married-filing-separately
How to start another return in the Online version
https://ttlc.intuit.com/questions/1894512-how-do-i-start-a-second-return-in-turbotax-online
To compare Joint to MFS. If you are using the Online version, do NOT change anything on your return. You would have to start with a new account and do a test return. You don't have to pay unless you want to print it out. So you might need 3 accounts, one for Joint and two MFS, one for each spouse.
How to Compare Joint to Married Filing Separately
https://ttlc.intuit.com/questions/2895312-how-can-we-compare-married-filing-jointly-with-married-filing-separately
How to start another return in the Online version
https://ttlc.intuit.com/questions/1894512-how-do-i-start-a-second-return-in-turbotax-online