How do I work on two returns at once, without having to file the first one?

[Mike9241]

clarify. online only allows one return per account. a second return started in the same account erases the first, 

[VolvoGirl]

Yes you can work on different returns.  You can start another return in TurboTax Online by:
Logging out if you are in your account
Choose what TurboTax Online product you want to use for the second return
https://turbotax.intuit.com/personal-taxes/compare/online

Create your account screen
Set up a new login for the second return
Start working on the new return

Or use the Desktop program. The Desktop program can do unlimited returns and efile 5 for free. And you can use any Desktop version, they all have the same forms. So you could use a lower version than you might need in the Online version.