The CD/download product installed on your computer can be used to file multiple tax returns and efile up to 5 federal returns for one purchase price. 

The online product can only be used to prepare and file one return on each account.

What defines a single account?  I used the same email address and phone number with 2 different login names and was able to file each last year.  However, this year only my daughters login works.  Mine brings up a brand new turbotax return and has none of my 15 years worth of returns.  Did creating her account with the same identifying info overwrite mine?  One would think that th SS would be the main/unique identifier.

@vlmedlyn 

With online TurboTax you get ONE return per fee.  You can use the same email for up to five accounts, but you need separate accounts and user IDs for each return you purchase.

When you use Online TurboTax, you get one return per fee.  Each return needs its own account and user ID.   If you use the same account and user ID for a second return, you overwrite the first one and lose it forever.

When you use Desktop TurboTax, which you install from a CD or download to your own hard drive, you can prepare and e-file multiple returns for the cost of the software.  You can e-file up to 5 Federal returns—more if you mail the additional ones.  If you have multiple returns to prepare for family members, Desktop is more cost effective.

https://ttlc.intuit.com/questions/1901306-how-many-times-can-i-e-file-using-the-turbotax-cd-or-downl...

https://ttlc.intuit.com/questions/2942039-what-s-the-difference-between-turbotax-online-and-the-turb...

https://ttlc.intuit.com/questions/2750704-what-are-the-advantages-of-the-turbotax-cd-download-softwa...

Do I have to use the cd version on the same computer or can I provide the key to other computers?

@GeorgePBurdell83 You can download your software to other computers that you own.   You will still have a limit of five federal e-files in total.  Any others must be printed, signed and mailed.