If you are using the Online version, you would have to do a separate online account (with a different user ID) for each federal return you want to prepare and purchase for each (if you need to use a paid version of the online software). But you can purchase the desktop version and do multiple returns within it.
You can still use your same email address if you want to get notifications, but the username must be a new one for each online account you create. If you do another return under the same username, it will override the one you already filed and lose everything for that return.
The CD/Download (desktop version) product is a better overall value for people who prepare tax returns for their friends and family. This one will allow you to prepare and print unlimited federal returns and e-file up to five at no extra cost. You can find the desktop versions here https://turbotax.intuit.com/personal-taxes/cd-download/
