If I bought the Costco version of turbotax can i start my taxes online and then add a code to show I already paid for it when I finish my taxes?

If you bought a CD at Costco and do not have a CD drive, look to see if there is a piece of paper inside the box that has a telephone number on it where you can request a download.   If not, you can phone TurboTax Support on Monday, and they will place a download in your account.  See this FAQ:

https://ttlc.intuit.com/questions/2590568-i-bought-the-cd-but-my-computer-doesn-t-have-a-cd-drive

You are welcome to begin a return Online for free if you wish, but there is no obligation to finish it online when the download is a better product, and you already paid for the desktop product.   You "could" talk to TurboTax Customer Support to see if they would let you finish online, but I'm not sure why someone would want to do that.  The download is a more fully-featured product than the online version.   You can even move what you've started online into the download product to finish. (steps to do that are in the FAQ down below).  

Also note that some Online editions cannot prepare all the forms.  For instance, Online Deluxe cannot handle Schedule C,D,E,F, or enter K-1 info.  Online Premier cannot handle Schedule C or F.  While ALL of the desktop (CD/download) versions can handle all of those forms.   The desktop version also has Forms Mode (which Online does not), and printing/viewing/archiving is easier in the desktop version, and you don't have a limit on future access to your files like the Online version, since you control all of them on your computer.  The desktop product also allows for multiple Federal returns, and your desktop version may already include a state program to prepare multiple state returns (of that one state).  In the Online product, a state return would be an extra 36.99 (39.99 later in filing season.)

So if you want to use Online instead, that would have to be an arrangement between you and Customer Support.

Once you have the download program installed, you can move the data you have prepared online into your desktop product so you don't have to start over.  Here's how:

https://ttlc.intuit.com/replies/3302260

I bought Turbotax Premier at Costco. When ready to file, I was asked how I want to pay. Turbotax charges an extra fee if you pay out of your refund, so pay with your credit card and you will only be charged the extra for your state. It's cheaper than paying using your refund. It took me an hour to figure that out with help from a human.

I had the same situation. Still not able to fix it after reading all the replies. I guess I have to start over. Will NOT use Turbo tax next year.