It depends on which product you are looking at.
If you are interested in TurboTax Online, each return is paid for separately. The fee depends on the version of TurboTax Online that you are using, though you don’t have to use the same version for all your returns. Premier and Self-Employed offer a discount on the spouse’s return, if you prepare them together. You will be asked to pay before you can file or print your return. If you have a prepaid code, it can be used at any time, however, codes for 2017 are only good for 2017, and can’t be used for previous year’s returns or for future year’s returns.
There is a CRA limit of 20 returns per computer when using NETFILE, so even if you use TurboTax Online Free, you can only do a maximum of 20 returns.
If you are interested in TurboTax CD/Download, you pay a fee upfront for a set number of returns. You can also purchase more returns for an additional fee, but the CRA limit of maximum of 20 returns still applies. The installation keys are only good for the year and version of the software that you buy. If you buy a 2017 edition of TurboTax CD/Download, you can still use it in future years, but you will only be able to create/edit returns for the 2017 tax year.